Oh, and I got Winamp 5 to start working again!!!
I figured it out: somehow, during my "normal use" of Winamp 5, files or registry keys were corrupted. I uninstalled Winamp 5, then installed Winamp 2.95 in the same folder. When I opened Winamp 2, it gave an end task message without showing anything. I uninstalled Winamp 2, which deleted the entire folder. Then I installed Winamp 5.09, and everything works like a charm again.
So try the same method with Firefox..