I use Firefox mobile (not Focus). My big complaint is the same complaint I have about Windows, Android, iOS, and most other software actually. Too many UI changes, too often. I'm not against change: I loved Win 8 right away. I'm against making and undoing changes willy-nilly, and never giving us a choice in what works best for us. How much bloat would that really be, letting us like make Start bigger (full screen) in 11?
It took ages for the new extension catalog to grow, but it's mostly there now.