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Extensions, or add-ons, can modify and enhance the capability of a browser. Extensions for Firefox are built using the WebExtensions API cross-browser technology.
The technology for extensions in Firefox is, to a large extent, compatible with the extension API supported by Chromium-based browsers (such as Google Chrome, Microsoft Edge, Opera, Vivaldi). In most cases, extensions written for Chromium-based browsers run in Firefox with just a few changes.
Whether you're just beginning or looking for more advanced advice, learn about how extensions work and use the WebExtensions API from our extensive range of tutorials and guides.
Get comprehensive details about the methods, properties, types, and events of the WebExtensions APIs and full details about the manifest keys.
Discover how to build and publish extensions for Firefox: get the lowdown on developer tools, publication and distribution, and porting on Extension Workshop.
Note: If you have ideas or questions or need help, you can reach us on the community forum or in the Add-ons Room on Matrix.
Discover what extensions can do before building your first extension and your second extension. Learn about the anatomy of an extension and get an overview of the extension development and publication workflow, Firefox style. Explore a little deeper with a comprehensive selection of example extensions that you can run right in Firefox. Continue your learning by discovering a list of resources to follow.
Get detailed information on the concepts that underpin extensions.
Discover all the user interface components you can use in your extensions, with coding examples and tips.
A range of tutorials to get you started on specific aspects of extension development.
When you are ready to create your extension for Firefox or port your Chrome extension, head over to Extension Workshop. It has details on:
Get comprehensive details about the methods, properties, types, and events for all the JavaScript APIs. There is also detailed information about the compatibility of each API with the major browsers. Most reference pages also include coding examples and links to the extension examples that use the API.
Get full details about the manifest keys, including all their properties and settings.
This page was last modified on Oct 8, 2026 by MDN contributors.
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