Firefox theme has brought my Linux to it's knees
 

I have several Gnome themes for Firefox and when I originally downloaded them, one had a warning to ONLY use it with a certain Gnome theme or it would break Firefox but I couldn't remember which theme.
Well I no longer use Gnome, I'm on KDE and I tried using one of the themes and unfortunately, it seems I used the the one I shouldn't have and indeed Firefox was totally messed up.
The problem is, it hasn't only messed up Firefox, it has messed up every single GTK based program.
Now whenever I try to run anything GTK based (and a lot of the things I use are) they either don't launch at all or they do launch but with badly deformed windows and in most cases it freezes my computer up completely.
Is there anything I can do to sort this out?
I'm not a Linux expert so if I need to re-install anything could someone tell me what commands I would need to type into the console since I normally do all installing via Synaptic and since that's GTK based...