One of the hard things is to troubleshoot when you can't duplicate the problem.
Have you tried deleting your Firfeox settings. First quit Firefox. If you have
bookmarks to save you can use a service like Foxmarks (from Mozilla Add-ons) or
you can same the bookmarks.html file in your /.mozilla/firefox/default/ folder.
To see your hidden folders press Control-H in Nautilus file manager. Just
navigate to that place and drag that file onto your desktop. Then delete the
whole Firefox folder. Then restart Firefox. It will recreate your settings
folder. If it is still messed up then I would remove it completely in Synaptic
and re-install it. Once it is working again, just drag your bookmarks from your
desktop back to where it came from and it will replace the recently created one.

If this does not work, then consider using Flock, Opera or SeaMonkey until
Firefox works to your satisfaction. Flock can be found at Getdeb.net. Opera can
be found on their site. SeaMonkey is in the repos. You can also get Safari to
work in Wine and Chrome works if you get it from Codeweavers. It is called
Chromium. www.codeweavers.com/services/ports/chromium/