firefox crashed with signal 5 in _XError()

[Lafa]

Binary package hint: firefox-3.5

I was closing the tabs and firefox just crashed

ProblemType: Crash
Architecture: amd64
CrashCounter: 1
Date: Sun Aug 23 00:11:43 2009
DistroRelease: Ubuntu 9.10
ExecutablePath: /usr/lib/firefox-3.5.2/firefox
Package: firefox-3.5 3.5.2+nobinonly-0ubuntu2
ProcCmdline: /usr/lib/firefox-3.5.2/firefox https://bugs.launchpad.net/ubuntu/+source/gnome-do/+filebug/ou3qHFLeNJg3l32LWUJcjYAwhRr?field.title=Do.exe+crashed+with+signal+5+in+_XError%28%29
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-6.26-generic
Signal: 5
SourcePackage: firefox-3.5
StacktraceTop:
 ?? () from /usr/lib/libgdk-x11-2.0.so.0
 _XError () from /usr/lib/libX11.so.6
 ?? () from /usr/lib/libX11.so.6
 _XReply () from /usr/lib/libX11.so.6
 XTranslateCoordinates () from /usr/lib/libX11.so.6
Title: firefox crashed with signal 5 in _XError()
Uname: Linux 2.6.31-6-generic x86_64
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare vboxusers