Shoutbox

It might be a profile problem, possibly. So if you want to try the following:
1. Select Start > Run...
2. Type '%appdata%' (without quotes) and hit Enter.
3. Navigate into Mozilla\Firefox\Profiles.
4. Optional: Go into each folder and copy 'bookmarks.html' (i.e. back up your Favourites).
5. Delete ALL folders in Profiles with Firefox CLOSED.
6. Start up Firefox and make a new profile.

If you backed up a bookmarks.html file, then you can restore it by going to the Profiles folder like above, and placing bookmarks.html in what should be the only folder in there.

Hope this helps