I am having the same problem. Right now I can't get google talk to show up, or explorer windows (not Internet Explorer)... Skype, ZoneAlarm, you name it. Nothing will show up on top of Firefox.
Yes, I have a lot of links open in Firefox and it is using 85 megs, but I have 1.5 gigs of ram in this computer, and I never had this problem before upgrading to FireFox 2.0
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