I'm perfectly happy with Firefox, both desktop and mobile. It works very well and I never have problems with it. It blocks ads on mobile and chrome doesn't. As far as I have seen, it's fast. I don't notice a difference on the rare occasion I open chromium to check and see that some application will look the same for a client as it does for me. But I guess it's always true: people go out of their way to complain, but…
I'll push back a little bit on this. To preface, I have also been at least reasonably happy with Fenix on Android, although I am frustrated that the add-ons are still limited. I don't feel like I have a lot of friction, the UI works well enough for what I need it to do, and I have pretty much no desire to switch to another browser. And I regularly get annoyed at the level of scrutiny and amount of bad-natured critici…
However, FireFox mobile could always be better. I really hope that Mozilla keeps listening to the users to figure out how to make the browsers better, especially when they have so many engineers that they seem to constantly shuffle the UI around just to give them work to do. There's plenty of actual improvements to make, and more options to give users with different preferences, and that should be where Mozilla spends engineer time with such a mature product. Instead of rewriting the browser every couple of years because the previous one was a mess.