Gnome browser addon for installing extensions does not work on Firefox in Ubuntu 21.10 [duplicate]
It's because when you installed/upgraded to 21.10, the Software Updater uninstalled your previous .deb version of Firefox, and installed a SNAP version of Firefox.
There are two possible ways to fix this...
-
Start the
Ubuntu Softwareapplication and search for "Firefox". You'll find two of them. One will show as installed... that would be the SNAP version. Uninstall it and install the other (.deb version of) Firefox. -
Or, using the command line in
terminal:sudo snap remove firefoxsudo apt updatesudo apt install firefox