I am running FireFox 18.104.22.168 and it rocks, but the RAM usage of it tends to climb really high during the day. Not too long ago, I found out by accident that if your FireFox crashes and then you start it up again it will ask you if you would like to restore the previous session. How bad-ass is that? I know, I know. But what's really cool that just occurred to me is that you can use this feature to control the RAM that FireFox uses.
My FireFox process was just hovering at about 250 MEGs of RAM usage. That's a ton or RAM (I don't have a crazy amount on this computer). I also have a good number of windows and tabs open as well for development, email, ColdFusion news feeds, etc. Well, now instead of closing them all down, then re-opening them manually, I just go in, Kill the FireFox process (which kills all the windows at once) and then restart FireFox which will in-turn, restore the session that was just running.
Doing this, the FireFox RAM usage went from about 250 MEGs down to about 95 MEGs and I hardly had to push a few buttons. Now, granted, this is a total misuse of the feature and probably of Window's task manager, but when my machine starts to drag, it just has to be done.