In at least one way, FF has been bloated all along.
Every time I've used any version of FF for the last four years, once it's been running for an hour or more it starts getting these little halts/pauses where the whole browser and UI freeze for half a second every 10-30 seconds. It gets worse the longer it's been open and the more pages i've opened. I've seen it on macs, windows, and linux. I've seen it on every machine I've ever used FF on. It is independent of all plugins and add-ons because it happens in a bare browser. I don't know what causes it, but intuitively it feels like garbage collection meets a bad memory leak.
It makes video unwatchable, which is pretty much death to a browser in today's world. Incidentally, it's happened three (now four) times while writing this post.
I've seen at least 5 bug reports and at least 10 threads in the Mozilla support forum. In every case, the developers/support people seem to not understand, or not believe that it's real, yet I've (another pause there) seen it on dozens of different computers and platforms, and never met a single computer with FF that *didn't* reproduce the problem. No matter how many bug reports get filed, this problem in FF never gets fixed.
And yet, I depend on my plugins for both browsing and developing. As it is, I use FF for almost everything, but I have to switch browsers to watch video, which is really annoying, and restart FF every (another pause there) three hours, which is even more annoying. /rant off