hi, for no particular reasons I cannot longer execute mozilla-thunderbird under Xfce. I tried to start it from the terminal, but I still have the problem: the whole X server seems to freeze (except from the pointer), but if I'm playing an MP3, I can still hear the music. Under Gnome I have not this kind of problem. Under Xfce I use the gnome-panel and I've disabled the xfce panel.
Really hard to tell with so little information. Do you run nVidia proprietary drivers? Some version where showing similar symptoms because of accelerated XRender. Otherwise, can you elaborate on the gnome-panel vs. xfce-panel issue? Did you have to switch to the gnome-panel because of this issue or is this totally unrelated? Maybe it's just an settings that beaks thunderbird. Log out from xfce, try renaming ~/.config/xfce4 to /.config/xfce4.old and log in xfce again to see if the problem still shows.
Moving invalid bugs to the /dev/null product.