Firefox did flash me a notification - in advance - yesterday (maybe because I have an account?) and I had already seen mention of this elsewhere so had disabled play store auto updates and I've removed my Master Password for now, just so my passwords don't get blitzed.
I could probably live with the new version - I use uBlock Origin and Privacy Badger to block ads and trackers and they are available in the new version (though I'd be unsurprised if Badger needed to relearn all the trackers it blocks.
However the lack of back/forward buttons (if true) would be a complete bummer - how else do you get back to the Register home page from here?.
I also understand that they haven't enabled about:config which would mean I have no control over my DNS (amongst other things): I do use DoH (via Nebulo) but avoid Cloudflare (the company whose Chief Security Officer was previously sacked by Uber).
On my PC's Firefox-esr (LTS) I have three months overlap of the old and the new version, so I don't get bumped into upgrading. On Android, not only do they stop supporting the old version for security immediately they hit you with an automatic upgrade.
For now I'm sitting fast on the old version. Any suggestions for a good alternative mobile browser? Don't say Chrome.