That may be in part because Firefox's share in mobile is minuscule. However Firefox has something called user agent switching (I think that's what it's called) which can make Firefox say "Oh hi there web site. I'm Internet Explorer or Chrome or whatever"even though it's Firefox. That visit would also be logged as Chrome or Internet Explorer or whatever I'd guess. I wonder if that accounts for some of Firefox's apparent decline. Or maybe not. As far as Firefox not working with certain web sites I kinda thought Firefox has privacy guards that some web site don't want to cooperate with. "What do you mean we can't track you?" Restarting in Safe Mode has worked for me.