I'm sure you thought of this but what plugins are you using? I am on win7 with the latest non-beta firefox and the only issue I have is that when saving an image from the browser sometimes the "New Folder" button produces a New Folder but it doesn't show up in the dialog box. And this may easily be a win 7 problem and not firefox. Otherwise ff seems stable on my box. Dual core, 4gb ram.
I don’t have any plugins. Straight install and use. It very well could be a 7 issue since this happens on all three installs I have. The browser will first hang, then crash and restart and it asks if I want to restore my session or start new. I pretty much only go to drudge, FR, gmail and facebook. I do click news links from FR and drudge. I do not usually venture out beyond that on a regular basis. I have a few sites I frequent and that’s it. Not sure the cause. For the most part firefox has been stable. on XP I found it to be rock solid. So far on 7 though, several crashes a day. The one thing I like is I do not lose my spot when it does crash as it restores my tabs.