This bug has been reported on Ubuntu Launchpad as:
https://bugs.launchpad.net/bugs/601997

xfdesktop crashed with SIGSEGV in atk_action_get_n_actions()

something crashed to login and this came up when logged back in and opened FF but that crashed

Package: xfdesktop4 4.6.1-1ubuntu3

Uname: Linux 2.6.32-23-generic i686

Architecture: i386

Distribution release: Xubuntu 10.04 "Lucid Lynx" - Release i386 (20100429)

ProcEnviron:
 SHELL=/bin/bash
 LANG=en_US.utf8

SegvAnalysis:
 Segfault happened at: 0x3a3615 <atk_action_get_n_actions+37>: cmp (%edx),%eax
 PC (0x003a3615) ok
 source "(%edx)" (0x00000001) not located in a known VMA region (needed readable region)!
 destination "%eax" ok
SegvReason: reading NULL VMA

Signal: 11

StacktraceTop:
 atk_action_get_n_actions (obj=0x83b32a0) at atkaction.c:84
 gtk_label_recalculate (label=<value optimized out>)
 IA__gtk_label_set_text (label=0x8225bb0,
 IA__gtk_tooltip_set_text (tooltip=0x81f6e78,
 xfdesktop_icon_view_show_tooltip (widget=0x81fd050, x=311,

Stacktrace available:
http://launchpadlibrarian.net/51423648/Stacktrace.txt