Google Chrome extensions in Firefox

If there is such a beast, even Mozilla developers don't know about it!

Many Chrome "extensions" are just Greasemonkey scripts, and these can be used with the Greasemonkey extension or compiler on Firefox with no changes.

Unfortunately, extensions that use other APIs must be ported. If you're looking to port a Chrome extension to Firefox, or planning to write one for both, take a look at Mozilla's new Jetpack extension API, which was designed to work in a manner similar to the way Chrome's extensions work, but still offer the vastly increased access to the browser the original Firefox API is known for.

As Mozilla is preparing its next-generation Servo engine, it's also phasing out older add-on technologies (e.g., XPCOM and XUL) and introducing new ones, like the WebExtensions API, which is "largely compatible with the model used by Chrome and Opera—to make it easier to develop extensions across multiple browsers". The WebExtensions API is nowhere near mature, so it's changing very fast; but if you're planning to port Chrome extensions over to Firefox with an eye towards the future, then I recommend installing Firefox Nightly and getting your hands dirty with the WebExtensions API today. You can read more about it in the links below.

• The Future of Developing Firefox Add-ons
• Porting Chrome Extensions to Firefox with WebExtensions
• WebExtensions API Reference