Since a few days, on my Ubuntu 13.10 (clean install),Firefox, Thunderbird and Chromium are not using the system theme anymore (Ambiance). They are grey, windows 95 like.
Gnome apps, however, work fine, except some of them showing a menu bar (which should not happen...).
I'm using stock Unity from the official repositoy.
I suspect an update broke something regarding theme settings, but I really don't see where to start...
Any help ?