Firefox 56 will be released on September 26th. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 56 for Developers, so you should also give it a look. Also, if you haven’t yet, please read our roadmap to Firefox 57.

Compatibility changes

Let me know in the comments if there’s anything missing or incorrect on these lists. We’d like to know if your add-on breaks on Firefox 56.

The automatic compatibility validation and upgrade for add-ons on AMO will run in a few weeks, so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 55.

Last stop!

Firefox 56 will be the last version of Firefox to support legacy add-ons. It’s the last release cycle you’ll have to port your add-ons to WebExtensions. Many planned APIs won’t make the cut for 57, so make sure that you plan your development timeline accordingly.

This is also the last compatibility overview I’ll write. I started writing these 7 years ago, the first one covering Firefox 4. Looking ahead, backwards-incompatible changes in WebExtensions APIs should be rare. When and if they occur, we’ll post one-offs about them, so please keep following this blog for updates.