Hey,
I had been so aggravated with this same problem... I did install Firefox (as you did) until I could figure out how to fix this.
I read somewhere that this problem could be caused by toolbars I'd installed (such as yahoo toolbar or aol toolbar). Well I tried uninstalling them but that didn't work... apparently there was still some "leftovers" of these toolbars even after the uninstall. So then I was on a search to find out how to completely remove the toolbars effectively.
I came across a site (
http://www.mrtech.com/cgi-local/msgb...=11&t=164;st=0) that had a tool for completely removing the toolbars:
http://www.mrtech.com/aolcleaner.exe
I did it and now I can have muliple IE windows open again!
So if you're still having that problem, you might want to try that.
Good luck!
