firefox crashed with SIGSEGV in _XReply()

[thebrunner]

Binary package hint: firefox-3.0

ProblemType: Crash
Architecture: i386
DistroRelease: Ubuntu 9.04
ExecutablePath: /usr/lib/firefox-3.0.5/firefox
Package: firefox-3.0 3.0.5+nobinonly-0ubuntu1
ProcCmdline: /usr/lib/firefox-3.0.5/firefox
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
Signal: 11
SourcePackage: firefox-3.0
StacktraceTop:
 _XReply () from /usr/lib/libX11.so.6
 XSync () from /usr/lib/libX11.so.6
 XRenderFindDisplay () from /usr/lib/libXrender.so.1
 XRenderFreePicture () from /usr/lib/libXrender.so.1
 ?? () from /usr/lib/libQtGui.so.4
Title: firefox crashed with SIGSEGV in _XReply()
Uname: Linux 2.6.28-6-generic i686
UserGroups: adm admin audio cdrom dialout dip floppy fuse lpadmin plugdev video

[Apport retracing service (apport)]

StacktraceTop:_XReply (dpy=0x8e31400, rep=0xbf9a97c0, extra=0, discard=1)
XSync (dpy=0x8e31400, discard=0) at ../../src/Sync.c:48
XRenderFindDisplay (dpy=0x8e31400)
XRenderFreePicture (dpy=0x8e31400, picture=71303919)
?? () from /usr/lib/libQtGui.so.4

[Dave (kn8aw)]

"firefox closed unexpectedly" appears on every reboot of kubuntu 9.04-a4, even though I have not had firefox running in previous session before reboot, nor did I try to start firefox after logging in.