Some programs crash randomly in Hoary

For some weeks I have some apps that crash without any reason. It concerns
Mozilla Thunderbird, Firefox, gvim and perhaps others Gtk applications (I don't
use Qt/KDE Apps)
For example, this morning Mozilla Thunderbird crash with this message.

tigrou@Lorien:~$ mozilla-thunderbird
selected locale: fr-FR
observe:
nothing here: null
observe called
FILE: [xpconnect wrapped nsIFile]DOUBLE-CLICK: 400 --> -1 THRESHOLD: 8 --> -1
The program 'Gecko' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadGC (invalid GC parameter)'.
  (Details: serial 323459 error_code 13 request_code 56 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

I was reading a message on usenet, but it also happens when I read mails or web
page with a RSS feed. Firefox crashes too, but I can't find any reason on web
page I see. (no flash, no java applet)

I don't know if it's related but I often have this message "art_render_invoke:
no image source given" in my ~/.xsession-errors