The current issue
From a Firefox user, I think the biggest problem with Firefox right now is its single process nature.
Firefox is currently the only browser with this problem, they really need to get electrolysis (multi-process Firefox) sorted out faster. For me the others out there aren't as good web browsers but they do some things better or faster.
I would use Chrome except Firefox has significantly better addons, a better bookmarking system and I don't trust google. (plus, I prefer a search box.. seriously.. all that wasted horizontal space by the silly location bar in Chrome)