Anatomy of an Extension

An extension is a simple collection of files that modify the browser’s appearance and behavior. It can add user interface elements, alter content, or perform background tasks that enhance browsing.

Learn more about extension anatomy

Manifest.json

Manifest.json

Build secure extensions

Mozilla takes the safety and privacy of its users very seriously. Be sure to review and follow these practices and policies so you can make your great idea a reality.

Build across browsers

Firefox is at the forefront of cross-browser compatibility. Firefox extensions are built using the WebExtensions API, so your creation will be accessible to users no matter what browser they use.

Learn about browser differences

Port a Google Chrome Extension

Your extension might already be compatible!

See if your extension works in Firefox. Simply upload your .crx file.

Test your extension

Need some extra help along the way?

When you build on Firefox, you build with a community of extension developers. And they’re eager to share their expertise and answer your questions.

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