Customize Firefox

Add-ons let millions of Firefox users enhance their browsing experience. If you know HTML, JavaScript, and CSS, you already have all the necessary skills to make a great add-on.

Learn How to Make an Add-on

Port a Chrome Extension

Firefox supports WebExtension APIs, which in most cases are compatible with the extension APIs supported by Chrome, Opera and Edge, so your extensions will run in Firefox with just a few changes.

Learn How

Publish Your Add-on

Have an add-on ready? Submit your extension or theme to be listed on or sign and distribute your extension on your own.

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Write one code base for many browsers

With the WebExtensions API, it’s easy to create extensions that will run on Firefox, Chrome, Opera, and Edge with only a few small changes. Learn more about the differences in extension development between the four major browsers and how you can make your extension cross-browser compatible.

View Best Practices for Cross-Browser Development

Latest News

Read more in our Blog


  • Web-Ext

    A command line tool to build, run, and test extensions.

  • Add-on Validator

    Automated code tests for your add-on.

  • Compatibility Test

    Check to see if your extension is compatible with Firefox.

  • Live Testing

    Temporarily install your extension in Firefox for live testing and debugging.