Problems running Mozilla with Xfce4

[goudal at enseirb.fr]

I have a big problem since I switched to xfce4 : Mozilla 1.4 crahes with the 
following code :

 X Error of failed request:  BadAccess (attempt to access private resource 
denied)
  Major opcode of failed request:  131 (MIT-SHM)
  Minor opcode of failed request:  1 (X_ShmAttach)
  Serial number of failed request:  23635
  Current serial number in output stream:  23636

It never happened with xfce3 it happens on a regular basis with xfce4.

f.g.