"In addition to that, there are also a few things that Firefox may have done wrong:
Constantly breaking the user experience with major overhauls"
Ye. One day my Firefox on mobile moved the URL bar to the bottom from the top. I don't even remember doing any update. It broke my muscle memory and it took months before I got used to it.For current users any UI changes that break the current UI "ABI" is bad. I guess the pressure to do pet projects is big internally as usual.