If current releases are anything to go by...
... probably a good time to leave.
I'm sure this post could cause a sea of down votes, whatever, but it's my opinion that firefox is heading down the wrong tracks as rapidly as the netscape which spawned it.
There's some sort of crazy version number 'catch up' going on with Chrome, or at least, that's how it seems.
I've had to cease using it on all my computers, because it seems to run so much slower than chrome.
As a former diehard fan of firefox, using it right from 0.6 (firebird) until a few months back, it's sad to see firefox seemingly in such poor shape - slow and bloated.
But hey, it could be just me ... or maybe not, most the other web devs I know have moved to chrome for similar reasons.