Sea Monkey is the replacement for the original Mozilla Web Application Suite.
Here is a link:
http://www.mozilla.org/projects/seamonkey/
Since IE works, the problem is with Firefox. I still suspect a corrupt registry key. But give a CLEAN reinstall of Firefox a try.
Either make a copy of the file bookmarks.html or use a utility such as URL Base to backup your book marks.
Uninstall Firefox.
Browse to, and delete the contents of all of these folders:
C:\Documents and Settings\{User Name}\Application Data\Mozilla
C:\Documents and Settings\{User Name}\Local Settings\Application Data\Mozilla
C:\Program Files\Mozilla Firefox
Caution: The above action will delete all passwords, form data, extensions, plug-ins, and themes.
Reboot, and install Firefox.
If you still have problems, it is time for a registry expert to go through and clean up the keys related to Firefox.
Chas