The fact that the folks over at Mozilla have slowly progressed into the mess of troglodytes that they are today should be but common knowledge at this point. That said, just in case you're ignorant to what these moronic sad sacks of human waste think about their users, let me fill you in on some of the stuff.
In the their infinite wisdom, these people have decided to redesign and "fancy the browser up," and in doing so have fucked several aspects of it in my opinion. Not only has the old, greatly appreciated by many, "compact density"-setting been semi-removed/deprecated. So if you want to enable compact density, as a new user, you now have to go to config:about and flip a hidden setting to get it back (browser.compactmode.show). But the stupidity doesn't end there, this mode is as of FF 90 bugged. Now if the website title contains certain special characters, the browser tab-bar expands to 3x~ times its "compact" size.
Like so many other things, it's completely useless to argue with these folks, too. Just take the recent Bugzilla entry for the Compact mode-deprecation as an example. Another example would be this bug report on Firefox's "megabar," detailing how one user experiences epilepsy symptoms due its implementation.
It's not just design these useless sacks of walking flesh can't do, they also can't fix bugs in general. I could list a number of (to me) severe to critical bugs that hasn't been fixed since they were reported, some over 5+ years ago. I don't want to list every single one, and frankly I just can't be bothered to. Still, one is related to the Activate Reader View-addon I used to make heavy use of. Due to the devs' inability to make the API consistent on that end, there's no way (through the API) for an addon to force the reader view active. Now, this wasn't exactly huge or in any way game breaking, but rest assured there's more critical ones out there, and plenty of 'em.
In conclusion, while I might loathe Chrom(e|ium)-based browsers, not least for their lack of support for a number of important addons and unavoidable links to Gooqle, the gang over at Mozilla comes closer by the day to making me consider switching browser.