How can they possibly spend a quarter billion a year?
The problem is that because they got such a big windfall from Google (now Yahoo) they had to come up with ways to spend all that. So they started stupid projects like FirefoxOS, waste resources maintaining ports for obsolete OSes like XP and Win2003, spend some of that money lobbying and so forth.
If they focus their goals better their budget will shrink and they'll be fine with the shrinking revenue. And maybe that focus would mean Firefox will improve and its share wouldn't keep declining - though I suspect that's an inevitable consequence of more and more web browsing happening on mobile devices. Firefox has no chance in mobile, because people will use the browsers their iOS and Android devices ship with. The only reason people went to Firefox was because IE was such a pig (and Linux users had no real choice) but the mobile browsers people use today are not really missing anything that Firefox can provide.