Earlier quoted context omitted.
FF’s UX around things not related to browsing is slightly worse on all platforms. It’s most obvious on iOS where some of the styles for your “library” just don’t work correctly on iPhone 10’s. I also think their model for managing non-browsing stuff is too complex comparatively. To access many things like history and bookmarks, you need to use the dropdown menu on the right, which has like 30 different options in it,…
I also avoid FF because of the UI. It's what I use on my PC, which doesn't get used much. If I have to VNC into a linux machine at work, I'll use it there as well. But that is even rarer. The last time I noticed a UI change, it was for the worse. The made the url/navigation/search bar get bigger when it had focus. To me that is pretty dumb, and I wish you could turn it off. Knowing Firefox you probably can, but a few…
Given those early reasons for favoring it, from my perspective it's mostly gotten worse since 2.0 came out.