I see this error too with Edgy but I don't see any reference to the Composite extension in my Xorg configuration so the only solution I have found is to remove flash plugin.
-- Consistent crash when visiting flash sites https://launchpad.net/bugs/35942 -- kubuntu-bugs mailing list kubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/kubuntu-bugs
