I've been using Windows 7 for a few weeks now. It's okay, other than the fact that I'm getting blue screens. Which I almost never got with XP, which is what I was using before. Used Vista for a couple of weeks, then upgraded back to XP. Might do the same with Windows 7.
Anyway, the point of my post here is that Firefox seems to be a lot better about memory management in 7 than in XP, for whatever reason. Haven't yet tried Chrome.