hedwards: Wow, that's a rather drastic reaction.
ThermioN: No, I switched back to 3.6 because Firefox 4 is using way too much RAM and it's keeps getting worse even if you don't do anything. +500 MB RAM after 1 hour of browsing with two tabs open is
not ok. And I doubt it's because I'm using NoScript, Flashblock and BetterPrivacy.
It is almost certainly because of either Flashblock or Better privacy, I'm not personally seeing that with NoScript. People frequently blame Firefox for what is a broken extension, in this case I think you'll find that if you disable the extensions that the memory use will go down drastically.
I have to really work hard to get the memory allocation to go over 300mb.