The UI toolkit "XUL" is something different from the extension API "XUL/XPCOM". And no, it's certainly not just an administrative deadline. For now, you can st

The UI toolkit "XUL" is something different from the extension API "XUL/XPCOM". And no, it's certainly not just an administrative deadline. For now, you can still tell Firefox Nightly to install legacy extensions, the vast majority of them are just by now completely broken, because Mozilla is ripping out all of that legacy code and refactoring what's left. Here's a list of all of the things that they can get rid of: https://bugzilla.mozilla.org/show_bug.cgi?id=1347507 https://bugzilla.mozilla.org/show_bug.cgi?id=1347507