firefox crashes and hangs a lot I find on Windows7. I have 3 installs of 7 and all three have the issue. I am completely up to date as firefox has pushed out a few stability updates as of late. I love their browser. I hate IE with a passion... Hope they fix the stability issues soon.
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.