See if this guide helps in just generally cleaning up your system:
http://www.epforums.org/panda-mans-m...888/index.html
If that doesn't help, export your FF bookmarks (Bookmarks > Organize bookmarks > File > Export) and uninstall FF and see if IE still does the same thing. If so, look at what updates have been installed the past few weeks (control Panel > add/remove programs > make sure "show updates" is check at the top). I'd remove any hotfixes and windows updates in the past few weeks (all the hotfixes and updates be listed under Windows XP - Software Updates), especially since M$ has been a bastard about installing them without user consent lately. Reboot and reinstall FF and see if the problem still persists.