this's depends on what extension that causes the problem,
and that may or may not help fixing the problem..
so pls don't take this personally, but it's going to be far easier for you to start over... i've done this about 100 times myself, during testing the Firefox and extensions. start a new profile will be the best and easiest way that i've found. it takes 5 mins... providing you already have all of the extensions that needs to be re-loaded on you HDD.
if you are certain that you installed "every" extensions as a profile-installed and not one of them is installed as a globally-installed extension, then you can backup your bookmarks.html, cookies.txt, etc, and remove the profile folder,
a new profile will be created on next Firefox starts.
if you are not sure, then do the backup of your bookmarks.html, cookies.txt, etc,
and uninstall the program and remove the profile folder, and start it over.
you can also try to manually uninstall the extension...
this how-to should still work..
http://kb.mozillazine.org/index.phtm...all_Extensions