> They eventually fixed it
And then broke it down, step by step. It used to be perfect but over the years gradually got changed/removed features that I loved, with no about:config option to get them back. Things like no menu button[1] (my device has a physical menu button), text reflow when zooming was removed, double tap to zoom to a paragraph now (sometimes?!) selects text instead of zooming, the tab you have open is no longer on the bottom side of the tab menu (it would slide open fast, as soon as your finger touched it and would feel super snappy; now there's some fancy animation)... etc.
It got to the point where I started looking for other browsers, but there just are no good options. Chromium sometimes bugs and uses 100% CPU for hours until I notice, and most other things are closed source. So I'm stuck with a mix of Firefox and Habit browser.
Habit seems to be what Firefox used to be: configure it any way you like (and it does a fantastic job at that). The trouble is that it's closed source and it has an inferior rendering engine, so I don't dare using it for things with a login that are valuable and it doesn't work for some websites.
Edit: by the way, the desktop story is completely different. I could never go without Firefox on non-mobile for various features (besides the privacy matter).
[1] What does that matter: Well, space (now there's two buttons next to the already-small address bar) and usability. I used to be able to hit the tab button without really looking. It was on the side of the screen, I'd just finger along that edge and I'd open my tab menu. Now I need to tap somewhere specific, and if I accidentally hit the menu button, I need to either reach over to the other side of the screen (on a 5.5" phone, that's a stretch for my thumb) or hit the back button (which would require shifting my phone, then touching it, then shifting back, all balancing it in one hand, oftentimes at least). How friggin' difficult is it to make an about:config setting to hide a button?