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It's created using familiar web-based technologies — HTML, CSS, and JavaScript. It can take advantage of the same web APIs as JavaScript on a web page, but an extension also has access to its own set of JavaScript APIs. This means that you can do a lot more in an extension than you can with code in a web page. Here are just a few examples of the things you can do:"/><meta property="og:url" content="https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions"/><meta property="og:title" content="What are extensions? - Mozilla | MDN"/><meta property="og:type" content="website"/><meta property="og:locale" content="en_US"/><meta property="og:description" content="An extension adds features and functions to a browser. It's created using familiar web-based technologies — HTML, CSS, and JavaScript. It can take advantage of the same web APIs as JavaScript on a web page, but an extension also has access to its own set of JavaScript APIs. This means that you can do a lot more in an extension than you can with code in a web page. 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Topics" class="sidebar-inner"><header class="sidebar-actions"><section class="sidebar-filter-container"><div class="sidebar-filter "><label id="sidebar-filter-label" class="sidebar-filter-label" for="sidebar-filter-input"><span class="icon icon-filter"></span><span class="visually-hidden">Filter sidebar</span></label><input id="sidebar-filter-input" autoComplete="off" class="sidebar-filter-input-field false" type="text" placeholder="Filter" value=""/><button type="button" class="button action has-icon clear-sidebar-filter-button"><span class="button-wrap"><span class="icon icon-cancel "></span><span class="visually-hidden">Clear filter input</span></span></button></div></section></header><div class="sidebar-inner-nav"><div class="in-nav-toc"><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#whats_next">What's next?</a></li></ul></section></div></div><div class="sidebar-body"> <ol> <li class="section"><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions">Browser extensions</a></li> <li> <details open=""> <summary>Getting started</summary> <ol> <li><em><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions" aria-current="page">What are extensions?</a></em></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension">Your first extension</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_second_WebExtension">Your second extension</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension">Anatomy of an extension</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Examples">Example extensions</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_next">What next?</a></li> </ol> </details> </li> <li> <details> <summary>Concepts</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API">JavaScript APIs</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_scripts">Content scripts</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Background_scripts">Background scripts</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Match_patterns">Match patterns</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_files">Work with files</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization">Internationalization</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_Security_Policy">Content Security Policy</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Native_messaging">Native messaging</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Differences_between_API_implementations">Differences between API implementations</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Chrome_incompatibilities">Chrome incompatibilities</a></li> </ol> </details> </li> <li> <details> <summary>User interface</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface">User interface</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Toolbar_button">Toolbar button</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Page_actions">Address bar button</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Sidebars">Sidebars</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Context_menu_items">Context menu items</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Options_pages">Options page</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Extension_pages">Extension pages</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Notifications">Notifications</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Omnibox">Address bar suggestions</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/devtools_panels">devtools panels</a></li> </ol> </details> </li> <li> <details> <summary>How to</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Intercept_HTTP_requests">Intercept HTTP requests</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Modify_a_web_page">Modify a web page</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Safely_inserting_external_content_into_a_page">Insert external content</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts">Share objects with page scripts</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Add_a_button_to_the_toolbar">Add a button to the toolbar</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Implement_a_settings_page">Implement a settings page</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_the_Tabs_API">Work with the Tabs API</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Bookmarks_API">Work with the Bookmarks API</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Cookies_API">Work with the Cookies API</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_contextual_identities">Work with contextual identities</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Interact_with_the_clipboard">Interact with the clipboard</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Extending_the_developer_tools">Extend the developer tools</a></li> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension">Build a cross-browser extension</a></li> </ol> </details> </li> <li> <details> <summary>JavaScript APIs</summary> <ol><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Browser_support_for_JavaScript_APIs">Browser support for JavaScript APIs</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/action">action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/alarms">alarms</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/bookmarks">bookmarks</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserAction">browserAction</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserSettings">browserSettings</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browsingData">browsingData</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/captivePortal">captivePortal</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/clipboard">clipboard</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/commands">commands</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contentScripts">contentScripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contextualIdentities">contextualIdentities</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/cookies">cookies</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/declarativeNetRequest">declarativeNetRequest</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools">devtools</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dns">dns</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dom">dom</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/downloads">downloads</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/events">events</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extension">extension</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extensionTypes">extensionTypes</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/find">find</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/history">history</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/i18n">i18n</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/identity">identity</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/idle">idle</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/management">management</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/menus">menus</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/notifications">notifications</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/omnibox">omnibox</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pageAction">pageAction</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/permissions">permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pkcs11">pkcs11</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/privacy">privacy</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/proxy">proxy</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime">runtime</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting">scripting</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/search">search</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sessions">sessions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sidebarAction">sidebarAction</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage">storage</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs">tabs</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/theme">theme</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/topSites">topSites</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/types">types</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/userScripts">userScripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webNavigation">webNavigation</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest">webRequest</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/API/windows">windows</a></li></ol> </details> </li> <li> <details> <summary>Manifest keys</summary> <ol> <li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json">manifest.json</a></li> </ol> <ol><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/action">action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/author">author</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background">background</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_action">browser_action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_specific_settings">browser_specific_settings</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_settings_overrides">chrome_settings_overrides</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_url_overrides">chrome_url_overrides</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/commands">commands</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_scripts">content_scripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy">content_security_policy</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/declarative_net_request">declarative_net_request</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/default_locale">default_locale</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/description">description</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/developer">developer</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/devtools_page">devtools_page</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/dictionaries">dictionaries</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/externally_connectable">externally_connectable</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/homepage_url">homepage_url</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/host_permissions">host_permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/icons">icons</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/incognito">incognito</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/manifest_version">manifest_version</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/name">name</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/offline_enabled">offline_enabled</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/omnibox">omnibox</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_host_permissions">optional_host_permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_permissions">optional_permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_page">options_page</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_ui">options_ui</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/page_action">page_action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/permissions">permissions</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/protocol_handlers">protocol_handlers</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/short_name">short_name</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sidebar_action">sidebar_action</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/storage">storage</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme">theme</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme_experiment">theme_experiment</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/user_scripts">user_scripts</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version">version</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version_name">version_name</a></li><li><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/web_accessible_resources">web_accessible_resources</a></li></ol> </details> </li> <li> <details> <summary>Extension Workshop</summary> <ol> <li><a href="https://extensionworkshop.com/documentation/develop/">Develop</a></li> <li><a href="https://extensionworkshop.com/documentation/publish/">Publish</a></li> <li><a href="https://extensionworkshop.com/documentation/manage/">Manage</a></li> <li><a href="https://extensionworkshop.com/documentation/enterprise/">Enterprise</a></li> </ol> </details> </li> <li class="section"><a href="/en-US/docs/Mozilla/Add-ons/Contact_us">Contact us</a></li> <li> <details> <summary>Channels</summary> <ol> <li><a href="https://blog.mozilla.org/addons">Add-ons blog</a></li> <li><a href="https://discourse.mozilla.org/c/add-ons">Add-ons forum</a></li> <li><a href="https://chat.mozilla.org/#/room/%23addons:mozilla.org">Add-ons chat</a></li> </ol> </details> </li> </ol> </div></div><section class="place side"></section></nav></aside><div class="toc-container"><aside class="toc"><nav><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#whats_next">What's next?</a></li></ul></section></div></nav></aside><section class="place side"></section></div></div><main id="content" class="main-content "><article class="main-page-content" lang="en-US"><header><h1>What are extensions?</h1></header><div class="section-content"><div class="notecard note"> <p><strong>Note:</strong> If you are already familiar with the basic concepts of browser extensions, skip this section to <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension">see how extension files are put together</a>. Then, use the <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions#reference">reference documentation</a> to start building your extension. Visit <a href="https://extensionworkshop.com/?utm_source=developer.mozilla.org&utm_medium=documentation&utm_campaign=your-first-extension" class="external" target="_blank">Firefox Extension Workshop</a> to learn more about the workflow for testing, publishing, and extensions for Firefox.</p> </div> <p>An extension adds features and functions to a browser. It's created using familiar web-based technologies — HTML, CSS, and JavaScript. It can take advantage of the same web APIs as JavaScript on a web page, but an extension also has access to its own set of JavaScript APIs. This means that you can do a lot more in an extension than you can with code in a web page. Here are just a few examples of the things you can do:</p> <p><strong>Enhance or complement a website</strong>: Use an add-on to deliver additional in-browser features or information from your website. Allow users to collect details from pages they visit to enhance the service you offer.</p> <p>Examples: <a href="https://addons.mozilla.org/en-US/firefox/addon/grammarly-1/" class="external" target="_blank">Grammarly for Firefox</a>, <a href="https://addons.mozilla.org/en-US/firefox/addon/enhancer-for-youtube/" class="external" target="_blank">Enhancer for YouTube</a>, and <a href="https://addons.mozilla.org/en-US/firefox/addon/control-panel-for-twitter/" class="external" target="_blank">Control Panel for Twitter</a>.</p> <p> <img src="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/grammarly-in-github-editor.png" alt="The Grammarly extension providing an edit hint in the GitHub editor." width="699" height="418" loading="lazy"> </p> <p><strong>Let users show their personality</strong>: Browser extensions can manipulate the content of web pages; for example, letting users add their favorite logo or picture as a background to every page they visit. Extensions may also enable users to update the look of the Firefox UI, the same way standalone <a href="https://extensionworkshop.com/documentation/themes/" class="external" target="_blank">theme add-ons</a> do.</p> <p>Examples: <a href="https://addons.mozilla.org/en-US/firefox/addon/tabliss/" class="external" target="_blank">Tabliss</a>, <a href="https://addons.mozilla.org/en-US/firefox/addon/styl-us/" class="external" target="_blank">Stylus</a>, and <a href="https://addons.mozilla.org/en-US/firefox/addon/emoji-sav/" class="external" target="_blank">Emoji</a>.</p> <p> <img src="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/tabliss_new_tab.png" alt="A new tab styled by the Tabliss extension showing a woodland picture with the time and a greeting message." width="700" height="408" loading="lazy"> </p> <p><strong>Add or remove content from web pages</strong>: You might want to help users block intrusive ads from web pages, provide access to a travel guide whenever a country or city is mentioned in a web page, or reformat page content to offer a consistent reading experience. With the ability to access and update both a page's HTML and CSS, extensions can help users see the web the way they want to.</p> <p>Examples: <a href="https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/" class="external" target="_blank">uBlock Origin</a>, <a href="https://addons.mozilla.org/en-US/firefox/addon/return-youtube-dislikes/" class="external" target="_blank">Return YouTube Dislike</a>, and <a href="https://addons.mozilla.org/en-US/firefox/addon/leechblock-ng/" class="external" target="_blank">LeechBlock NG</a>.</p> <p> <img src="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/ublock_origin_add_on.png" alt="uBlock origin pop-up showing blocked tracker statistics." width="711" height="513" loading="lazy"> </p> <p><strong>Add tools and new browsing features</strong>: Add new features to a taskboard, or generate QR code images from URLs, hyperlinks, or page text. With flexible UI options and the power of the <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions">WebExtensions APIs</a> you can easily add new features to a browser. And, you can enhance almost any website's features or functionality, it doesn't have to be your website.</p> <p>Examples: <a href="https://addons.mozilla.org/en-US/firefox/addon/worldwide-radio/" class="external" target="_blank">Worldwide Radio</a>, <a href="https://addons.mozilla.org/en-US/firefox/addon/flagfox/" class="external" target="_blank">Flagfox</a>, and <a href="https://addons.mozilla.org/en-US/firefox/addon/tomato-clock/" class="external" target="_blank">Tomato Clock</a>.</p> <p> <img src="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/worldwide_radio_extension.png" alt="The Worldwide Radio extension showing a list of radio stations for Canada, with RadioOne selected to play." width="711" height="681" loading="lazy"> </p> <p><strong>Games</strong>: Offer traditional computer games with offline play features or explore new game possibilities, such as incorporating gameplay into everyday browsing.</p> <p>Examples: <a href="https://addons.mozilla.org/en-US/firefox/addon/rpg-game-online-dedalium/" class="external" target="_blank">RPG Game - Dedalium by Loycom Games</a>, <a href="https://addons.mozilla.org/en-US/firefox/addon/solitaire-spider-freecell/" class="external" target="_blank">Solitaire Card Game</a>, and <a href="https://addons.mozilla.org/en-US/firefox/addon/2048-prime/" class="external" target="_blank">2048 Prime</a>.</p> <p> <img src="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/dedalium_popup.png" alt="The Dedalium pop-up showing play status and providing options to start a battle or adventure." width="711" height="695" loading="lazy"> </p> <p><strong>Add development tools</strong>: You may provide web development tools as your business or have developed a useful technique or approach to web development that you want to share. Either way, you can enhance the built-in Firefox developer tools by adding a new tab to the developer toolbar.</p> <p>Examples: <a href="https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/" class="external" target="_blank">aXe Developer Tools</a>, <a href="https://addons.mozilla.org/en-US/firefox/addon/web-developer/" class="external" target="_blank">Web Developer</a>, and <a href="https://addons.mozilla.org/en-US/firefox/addon/react-devtools/" class="external" target="_blank">Web React Developer Tools</a>.</p> <p> <img src="/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/axe_developer_tools_add_on.png" alt="The Axe accessibility testing extension showing accessibility issues found in a webpage." width="711" height="495" loading="lazy"> </p> <p>Extensions for Firefox are built using the <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions">WebExtensions APIs</a>, a cross-browser system for developing extensions. To a large extent, the API is compatible with the <a href="https://developer.chrome.com/docs/extensions/reference/" class="external" target="_blank">extension API</a> supported by Google Chrome and Opera. Extensions written for these browsers will in most cases run in Firefox or Microsoft Edge with just a few <a href="https://extensionworkshop.com/documentation/develop/porting-a-google-chrome-extension/" class="external" target="_blank">changes</a>.</p> <p>If you have ideas or questions, you can reach us on the <a href="https://discourse.mozilla.org/c/add-ons/35" class="external" target="_blank">Add-ons Discourse</a> or in the <a href="https://chat.mozilla.org/#/room/#addons:mozilla.org" class="external" target="_blank">Add-ons room</a> on <a href="https://wiki.mozilla.org/Matrix" class="external" target="_blank">Matrix</a>.</p></div><section aria-labelledby="whats_next"><h2 id="whats_next"><a href="#whats_next">What's next?</a></h2><div class="section-content"><ul> <li>Walk through the development of an extension in <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension">Your first extension</a>.</li> <li>Learn about the structure of an extension in <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension">Anatomy of an extension</a>.</li> <li>Try out some example extensions in <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/Examples">Example extensions</a>.</li> </ul></div></section></article><aside class="article-footer"><div class="article-footer-inner"><div class="svg-container"><svg xmlns="http://www.w3.org/2000/svg" width="162" height="162" viewBox="0 0 162 162" fill="none" role="none"><mask id="b" fill="#fff"><path d="M97.203 47.04c8.113-7.886 18.004-13.871 28.906-17.492a78 78 0 0 1 33.969-3.39c11.443 1.39 22.401 5.295 32.024 11.411s17.656 14.28 23.476 23.86c5.819 9.579 9.269 20.318 10.083 31.385a69.85 69.85 0 0 1-5.387 32.44c-4.358 10.272-11.115 19.443-19.747 26.801-8.632 7.359-18.908 12.709-30.034 15.637l-6.17-21.698c7.666-2.017 14.746-5.703 20.694-10.773 5.948-5.071 10.603-11.389 13.606-18.467a48.14 48.14 0 0 0 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3.324v4.868h1.864v3.044h-5.864v-7.884c0-2.423-.806-3.352-2.39-3.352-1.924 0-2.702 1.365-2.702 3.324v4.868h2.669v3.044H6.642v-3.044h1.863v-7.918H6.642V11.42h5.864v2.11c.839-1.489 2.3-2.39 4.252-2.39 2.02 0 3.878.963 4.566 3.01.778-1.862 2.361-3.01 4.566-3.01 2.512 0 4.812 1.522 4.812 4.84v6.402h1.863v3.044h-.005Zm9.036.307c-4.314 0-7.296-2.635-7.296-7.106 0-4.096 2.484-7.481 7.514-7.481s7.481 3.38 7.481 7.29c0 4.472-3.228 7.297-7.699 7.297Zm22.578-.307H51.942l-.403-2.11 7.7-8.846h-4.376l-.621 2.17-2.888-.313.498-4.907h12.294l.313 2.11-7.767 8.852h4.533l.654-2.172 3.167.308-.872 4.908Zm7.99 0h-4.191v-5.03h4.19v5.03Zm0-8.976h-4.191v-5.03h4.19v5.03Zm2.618 8.976 6.054-21.358h3.945l-6.054 21.358h-3.945Zm8.136 0 6.048-21.358h3.945l-6.054 21.358h-3.939Zm21.486.307c-1.863 0-2.887-1.085-3.072-2.792-.805 1.427-2.232 2.792-4.498 2.792-2.02 0-4.314-1.085-4.314-4.006 0-3.447 3.323-4.253 6.518-4.253.778 0 1.584.034 2.3.124v-.465c0-1.427-.034-3.133-2.3-3.133-.84 0-1.488.061-2.143.402l-.453 1.578-3.195-.34.549-3.224c2.45-.996 3.692-1.27 5.992-1.27 3.01 0 5.556 1.55 5.556 4.75v6.083c0 .805.314 1.085.963 1.085.184 0 .375-.034.587-.095l.034 2.11a5.432 5.432 0 0 1-2.524.654Z" fill="currentColor"></path></svg></a><ul class="footer-moz-list"><li class="footer-moz-item"><a href="https://www.mozilla.org/privacy/websites/" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Website Privacy Notice</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/privacy/websites/#cookies" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Cookies</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/about/legal/terms/mozilla" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Legal</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/about/governance/policies/participation/" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Community Participation Guidelines</a></li></ul></div><div class="page-footer-legal"><p id="license" class="page-footer-legal-text">Visit <a href="https://www.mozilla.org" target="_blank" rel="noopener noreferrer">Mozilla Corporation’s</a> not-for-profit parent, the <a target="_blank" rel="noopener noreferrer" href="https://foundation.mozilla.org/">Mozilla Foundation</a>.<br/>Portions of this content are ©1998–2024 by individual mozilla.org contributors. Content available under <a href="/en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license">a Creative Commons license</a>.</p></div></div></footer></div><script type="application/json" id="hydration">{"url":"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions","doc":{"isMarkdown":true,"isTranslated":false,"isActive":true,"flaws":{},"title":"What are extensions?","mdn_url":"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions","locale":"en-US","native":"English (US)","sidebarHTML":"\n <ol>\n <li class=\"section\"><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions\">Browser extensions</a></li>\n <li>\n <details open=\"\">\n <summary>Getting started</summary>\n <ol>\n <li><em><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions\" aria-current=\"page\">What are extensions?</a></em></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension\">Your first extension</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_second_WebExtension\">Your second extension</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension\">Anatomy of an extension</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Examples\">Example extensions</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_next\">What next?</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>Concepts</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API\">JavaScript APIs</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_scripts\">Content scripts</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Background_scripts\">Background scripts</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Match_patterns\">Match patterns</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_files\">Work with files</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization\">Internationalization</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_Security_Policy\">Content Security Policy</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Native_messaging\">Native messaging</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Differences_between_API_implementations\">Differences between API implementations</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Chrome_incompatibilities\">Chrome incompatibilities</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>User interface</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface\">User interface</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Toolbar_button\">Toolbar button</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Page_actions\">Address bar button</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Sidebars\">Sidebars</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Context_menu_items\">Context menu items</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Options_pages\">Options page</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Extension_pages\">Extension pages</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Notifications\">Notifications</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/Omnibox\">Address bar suggestions</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/user_interface/devtools_panels\">devtools panels</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>How to</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Intercept_HTTP_requests\">Intercept HTTP requests</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Modify_a_web_page\">Modify a web page</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Safely_inserting_external_content_into_a_page\">Insert external content</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts\">Share objects with page scripts</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Add_a_button_to_the_toolbar\">Add a button to the toolbar</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Implement_a_settings_page\">Implement a settings page</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Working_with_the_Tabs_API\">Work with the Tabs API</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Bookmarks_API\">Work with the Bookmarks API</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_the_Cookies_API\">Work with the Cookies API</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Work_with_contextual_identities\">Work with contextual identities</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Interact_with_the_clipboard\">Interact with the clipboard</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Extending_the_developer_tools\">Extend the developer tools</a></li>\n<li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension\">Build a cross-browser extension</a></li>\n </ol>\n </details>\n </li>\n <li>\n <details>\n <summary>JavaScript APIs</summary>\n <ol><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Browser_support_for_JavaScript_APIs\">Browser support for JavaScript APIs</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/action\">action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/alarms\">alarms</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/bookmarks\">bookmarks</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserAction\">browserAction</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browserSettings\">browserSettings</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/browsingData\">browsingData</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/captivePortal\">captivePortal</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/clipboard\">clipboard</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/commands\">commands</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contentScripts\">contentScripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/contextualIdentities\">contextualIdentities</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/cookies\">cookies</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/declarativeNetRequest\">declarativeNetRequest</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools\">devtools</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dns\">dns</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/dom\">dom</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/downloads\">downloads</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/events\">events</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extension\">extension</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/extensionTypes\">extensionTypes</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/find\">find</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/history\">history</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/i18n\">i18n</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/identity\">identity</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/idle\">idle</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/management\">management</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/menus\">menus</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/notifications\">notifications</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/omnibox\">omnibox</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pageAction\">pageAction</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/permissions\">permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/pkcs11\">pkcs11</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/privacy\">privacy</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/proxy\">proxy</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime\">runtime</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting\">scripting</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/search\">search</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sessions\">sessions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/sidebarAction\">sidebarAction</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage\">storage</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs\">tabs</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/theme\">theme</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/topSites\">topSites</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/types\">types</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/userScripts\">userScripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webNavigation\">webNavigation</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest\">webRequest</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/API/windows\">windows</a></li></ol>\n </details>\n </li>\n <li>\n <details>\n <summary>Manifest keys</summary>\n <ol>\n <li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json\">manifest.json</a></li>\n </ol>\n <ol><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/action\">action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/author\">author</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background\">background</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_action\">browser_action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/browser_specific_settings\">browser_specific_settings</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_settings_overrides\">chrome_settings_overrides</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/chrome_url_overrides\">chrome_url_overrides</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/commands\">commands</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_scripts\">content_scripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy\">content_security_policy</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/declarative_net_request\">declarative_net_request</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/default_locale\">default_locale</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/description\">description</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/developer\">developer</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/devtools_page\">devtools_page</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/dictionaries\">dictionaries</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/externally_connectable\">externally_connectable</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/homepage_url\">homepage_url</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/host_permissions\">host_permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/icons\">icons</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/incognito\">incognito</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/manifest_version\">manifest_version</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/name\">name</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/offline_enabled\">offline_enabled</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/omnibox\">omnibox</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_host_permissions\">optional_host_permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/optional_permissions\">optional_permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_page\">options_page</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/options_ui\">options_ui</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/page_action\">page_action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/permissions\">permissions</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/protocol_handlers\">protocol_handlers</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/short_name\">short_name</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sidebar_action\">sidebar_action</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/storage\">storage</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme\">theme</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/theme_experiment\">theme_experiment</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/user_scripts\">user_scripts</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version\">version</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/version_name\">version_name</a></li><li><a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/web_accessible_resources\">web_accessible_resources</a></li></ol>\n </details>\n </li>\n <li>\n <details>\n <summary>Extension Workshop</summary>\n <ol>\n <li><a href=\"https://extensionworkshop.com/documentation/develop/\">Develop</a></li>\n <li><a href=\"https://extensionworkshop.com/documentation/publish/\">Publish</a></li>\n <li><a href=\"https://extensionworkshop.com/documentation/manage/\">Manage</a></li>\n <li><a href=\"https://extensionworkshop.com/documentation/enterprise/\">Enterprise</a></li>\n </ol>\n </details>\n </li>\n <li class=\"section\"><a href=\"/en-US/docs/Mozilla/Add-ons/Contact_us\">Contact us</a></li>\n <li>\n <details>\n <summary>Channels</summary>\n <ol>\n <li><a href=\"https://blog.mozilla.org/addons\">Add-ons blog</a></li>\n <li><a href=\"https://discourse.mozilla.org/c/add-ons\">Add-ons forum</a></li>\n <li><a href=\"https://chat.mozilla.org/#/room/%23addons:mozilla.org\">Add-ons chat</a></li>\n </ol>\n </details>\n </li>\n </ol>\n","sidebarMacro":"AddonSidebar","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<div class=\"notecard note\">\n <p><strong>Note:</strong> If you are already familiar with the basic concepts of browser extensions, skip this section to <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension\">see how extension files are put together</a>. Then, use the <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions#reference\">reference documentation</a> to start building your extension. Visit <a href=\"https://extensionworkshop.com/?utm_source=developer.mozilla.org&utm_medium=documentation&utm_campaign=your-first-extension\" class=\"external\" target=\"_blank\">Firefox Extension Workshop</a> to learn more about the workflow for testing, publishing, and extensions for Firefox.</p>\n</div>\n<p>An extension adds features and functions to a browser. It's created using familiar web-based technologies — HTML, CSS, and JavaScript. It can take advantage of the same web APIs as JavaScript on a web page, but an extension also has access to its own set of JavaScript APIs. This means that you can do a lot more in an extension than you can with code in a web page. Here are just a few examples of the things you can do:</p>\n<p><strong>Enhance or complement a website</strong>: Use an add-on to deliver additional in-browser features or information from your website. Allow users to collect details from pages they visit to enhance the service you offer.</p>\n<p>Examples: <a href=\"https://addons.mozilla.org/en-US/firefox/addon/grammarly-1/\" class=\"external\" target=\"_blank\">Grammarly for Firefox</a>, <a href=\"https://addons.mozilla.org/en-US/firefox/addon/enhancer-for-youtube/\" class=\"external\" target=\"_blank\">Enhancer for YouTube</a>, and <a href=\"https://addons.mozilla.org/en-US/firefox/addon/control-panel-for-twitter/\" class=\"external\" target=\"_blank\">Control Panel for Twitter</a>.</p>\n<p>\n <img src=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/grammarly-in-github-editor.png\" alt=\"The Grammarly extension providing an edit hint in the GitHub editor.\" width=\"699\" height=\"418\" loading=\"lazy\">\n</p>\n<p><strong>Let users show their personality</strong>: Browser extensions can manipulate the content of web pages; for example, letting users add their favorite logo or picture as a background to every page they visit. Extensions may also enable users to update the look of the Firefox UI, the same way standalone <a href=\"https://extensionworkshop.com/documentation/themes/\" class=\"external\" target=\"_blank\">theme add-ons</a> do.</p>\n<p>Examples: <a href=\"https://addons.mozilla.org/en-US/firefox/addon/tabliss/\" class=\"external\" target=\"_blank\">Tabliss</a>, <a href=\"https://addons.mozilla.org/en-US/firefox/addon/styl-us/\" class=\"external\" target=\"_blank\">Stylus</a>, and <a href=\"https://addons.mozilla.org/en-US/firefox/addon/emoji-sav/\" class=\"external\" target=\"_blank\">Emoji</a>.</p>\n<p>\n <img src=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/tabliss_new_tab.png\" alt=\"A new tab styled by the Tabliss extension showing a woodland picture with the time and a greeting message.\" width=\"700\" height=\"408\" loading=\"lazy\">\n</p>\n<p><strong>Add or remove content from web pages</strong>: You might want to help users block intrusive ads from web pages, provide access to a travel guide whenever a country or city is mentioned in a web page, or reformat page content to offer a consistent reading experience. With the ability to access and update both a page's HTML and CSS, extensions can help users see the web the way they want to.</p>\n<p>Examples: <a href=\"https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/\" class=\"external\" target=\"_blank\">uBlock Origin</a>, <a href=\"https://addons.mozilla.org/en-US/firefox/addon/return-youtube-dislikes/\" class=\"external\" target=\"_blank\">Return YouTube Dislike</a>, and <a href=\"https://addons.mozilla.org/en-US/firefox/addon/leechblock-ng/\" class=\"external\" target=\"_blank\">LeechBlock NG</a>.</p>\n<p>\n <img src=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/ublock_origin_add_on.png\" alt=\"uBlock origin pop-up showing blocked tracker statistics.\" width=\"711\" height=\"513\" loading=\"lazy\">\n</p>\n<p><strong>Add tools and new browsing features</strong>: Add new features to a taskboard, or generate QR code images from URLs, hyperlinks, or page text. With flexible UI options and the power of the <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions\">WebExtensions APIs</a> you can easily add new features to a browser. And, you can enhance almost any website's features or functionality, it doesn't have to be your website.</p>\n<p>Examples: <a href=\"https://addons.mozilla.org/en-US/firefox/addon/worldwide-radio/\" class=\"external\" target=\"_blank\">Worldwide Radio</a>, <a href=\"https://addons.mozilla.org/en-US/firefox/addon/flagfox/\" class=\"external\" target=\"_blank\">Flagfox</a>, and <a href=\"https://addons.mozilla.org/en-US/firefox/addon/tomato-clock/\" class=\"external\" target=\"_blank\">Tomato Clock</a>.</p>\n<p>\n <img src=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/worldwide_radio_extension.png\" alt=\"The Worldwide Radio extension showing a list of radio stations for Canada, with RadioOne selected to play.\" width=\"711\" height=\"681\" loading=\"lazy\">\n</p>\n<p><strong>Games</strong>: Offer traditional computer games with offline play features or explore new game possibilities, such as incorporating gameplay into everyday browsing.</p>\n<p>Examples: <a href=\"https://addons.mozilla.org/en-US/firefox/addon/rpg-game-online-dedalium/\" class=\"external\" target=\"_blank\">RPG Game - Dedalium by Loycom Games</a>, <a href=\"https://addons.mozilla.org/en-US/firefox/addon/solitaire-spider-freecell/\" class=\"external\" target=\"_blank\">Solitaire Card Game</a>, and <a href=\"https://addons.mozilla.org/en-US/firefox/addon/2048-prime/\" class=\"external\" target=\"_blank\">2048 Prime</a>.</p>\n<p>\n <img src=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/dedalium_popup.png\" alt=\"The Dedalium pop-up showing play status and providing options to start a battle or adventure.\" width=\"711\" height=\"695\" loading=\"lazy\">\n</p>\n<p><strong>Add development tools</strong>: You may provide web development tools as your business or have developed a useful technique or approach to web development that you want to share. Either way, you can enhance the built-in Firefox developer tools by adding a new tab to the developer toolbar.</p>\n<p>Examples: <a href=\"https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/\" class=\"external\" target=\"_blank\">aXe Developer Tools</a>, <a href=\"https://addons.mozilla.org/en-US/firefox/addon/web-developer/\" class=\"external\" target=\"_blank\">Web Developer</a>, and <a href=\"https://addons.mozilla.org/en-US/firefox/addon/react-devtools/\" class=\"external\" target=\"_blank\">Web React Developer Tools</a>.</p>\n<p>\n <img src=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions/axe_developer_tools_add_on.png\" alt=\"The Axe accessibility testing extension showing accessibility issues found in a webpage.\" width=\"711\" height=\"495\" loading=\"lazy\">\n</p>\n<p>Extensions for Firefox are built using the <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions\">WebExtensions APIs</a>, a cross-browser system for developing extensions. To a large extent, the API is compatible with the <a href=\"https://developer.chrome.com/docs/extensions/reference/\" class=\"external\" target=\"_blank\">extension API</a> supported by Google Chrome and Opera. Extensions written for these browsers will in most cases run in Firefox or Microsoft Edge with just a few <a href=\"https://extensionworkshop.com/documentation/develop/porting-a-google-chrome-extension/\" class=\"external\" target=\"_blank\">changes</a>.</p>\n<p>If you have ideas or questions, you can reach us on the <a href=\"https://discourse.mozilla.org/c/add-ons/35\" class=\"external\" target=\"_blank\">Add-ons Discourse</a> or in the <a href=\"https://chat.mozilla.org/#/room/#addons:mozilla.org\" class=\"external\" target=\"_blank\">Add-ons room</a> on <a href=\"https://wiki.mozilla.org/Matrix\" class=\"external\" target=\"_blank\">Matrix</a>.</p>"}},{"type":"prose","value":{"id":"whats_next","title":"What's next?","isH3":false,"content":"<ul>\n <li>Walk through the development of an extension in <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension\">Your first extension</a>.</li>\n <li>Learn about the structure of an extension in <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Anatomy_of_a_WebExtension\">Anatomy of an extension</a>.</li>\n <li>Try out some example extensions in <a href=\"/en-US/docs/Mozilla/Add-ons/WebExtensions/Examples\">Example extensions</a>.</li>\n</ul>"}}],"toc":[{"text":"What's next?","id":"whats_next"}],"summary":"An extension adds features and functions to a browser. It's created using familiar web-based technologies — HTML, CSS, and JavaScript. It can take advantage of the same web APIs as JavaScript on a web page, but an extension also has access to its own set of JavaScript APIs. This means that you can do a lot more in an extension than you can with code in a web page. Here are just a few examples of the things you can do:","popularity":0.0078,"modified":"2024-11-21T19:49:47.000Z","other_translations":[{"locale":"de","title":"Was sind Erweiterungen?","native":"Deutsch"},{"locale":"es","title":"¿Qué son las extensiones?","native":"Español"},{"locale":"fr","title":"Qu'est-ce que les WebExtensions ?","native":"Français"},{"locale":"ja","title":"拡張機能とは何か？","native":"日本語"},{"locale":"ko","title":"What are extensions?","native":"한국어"},{"locale":"pt-BR","title":"O que são extensões?","native":"Português (do Brasil)"},{"locale":"ru","title":"Что такое расширения?","native":"Русский"},{"locale":"zh-CN","title":"扩展是什么？","native":"中文 (简体)"},{"locale":"zh-TW","title":"何謂附加元件？","native":"正體中文 (繁體)"}],"pageType":"guide","source":{"folder":"en-us/mozilla/add-ons/webextensions/what_are_webextensions","github_url":"https://github.com/mdn/content/blob/main/files/en-us/mozilla/add-ons/webextensions/what_are_webextensions/index.md","last_commit_url":"https://github.com/mdn/content/commit/93b34fcdb9cf91ff44f5dfe7f4dcd13e961962da","filename":"index.md"},"short_title":"What are extensions?","parents":[{"uri":"/en-US/docs/Mozilla","title":"Mozilla"},{"uri":"/en-US/docs/Mozilla/Add-ons","title":"Add-ons"},{"uri":"/en-US/docs/Mozilla/Add-ons/WebExtensions","title":"Browser extensions"},{"uri":"/en-US/docs/Mozilla/Add-ons/WebExtensions/What_are_WebExtensions","title":"What are extensions?"}],"pageTitle":"What are extensions? - Mozilla | MDN","noIndexing":false}}</script></body></html>