Mozilla is super annoying about constantly changing (and some, including me, say ruining) the UI for no apparent reason. On my Linux Mint machine I set the updater to ignore Firefox for the time being, beginning with FF 89, because of what I read was coming.
It’s apparently still - temporarily - possible to revert some of the damage. The site ghacks.net, which is a good place to keep watch on impending Firefox changes, has the instructions:
This might help…until it’s too late:
about:config
browser.proton.enabled false