Firefox’s wounds have been self-inflicted.
No surprise that almost as many folks are using pre-XP flavors as are using Vista. Vista was always seen as garbage with most sales coming from factory installs.
I haven’t tried 8.1, but limited experience with 8 showed that it must have been developed by the Vista team. I’ll stick with 7 at this point until something better comes along.
I’ve been on 8.1 since it was released (free upgrade from 8) and IMO it’s as good as Windows 7.
The funny thing is they are all versions of Windows NT.