We allocate an XImage here: http://lxr.mozilla.org/seamonkey/source/gfx/src/gtk/nsImageGTK.cpp#717 and then use it without checking to see if it was actually allocated. This is causing crashes for me; I can only reproduce them using my own skin though (I can add the URL for that if you think I'm at fault). I'm attaching a patch which just checks the ximage with an assertion after we call XGetImage. Assigning to tor based on cvs blame.
bug 52980 crash in libgfx_gtk.so
*** This bug has been marked as a duplicate of 52275 ***