Maybe the same bug. 
Firefox is started in gdb. When I close the GUI of firefox to exit, gdb catched this  SIGSEGV:


[Thread 0x7fffdb2ff910 (LWP 17777) exited]                   
[Thread 0x7fffe6ce4910 (LWP 25702) exited]                   

Program received signal SIGSEGV, Segmentation fault.
IA__g_type_check_instance (type_instance=0x7fffd0310a80) at /build/buildd/glib2.0-2.22.2/gobject/gtype.c:3802
3802    /build/buildd/glib2.0-2.22.2/gobject/gtype.c: No such file or directory.                             
        in /build/buildd/glib2.0-2.22.2/gobject/gtype.c                                                      
(gdb)                                                                                                        
(gdb) backtrace                                                                                              
#0  IA__g_type_check_instance (type_instance=0x7fffd0310a80) at /build/buildd/glib2.0-2.22.2/gobject/gtype.c:3802
#1  0x00007ffff251499b in IA__g_signal_handlers_disconnect_matched (instance=0x7fffd0310a80, mask=24, signal_id=0, detail=0, closure=0x0, 
    func=<value optimized out>, data=0x7fffd12af200) at /build/buildd/glib2.0-2.22.2/gobject/gsignal.c:2667                               
#2  0x00007fffdc2b4e93 in ?? () from /usr/lib/gtk-2.0/2.10.0/immodules/im-xim.so                                                          
#3  0x00007fffdc2b4f2b in ?? () from /usr/lib/gtk-2.0/2.10.0/immodules/im-xim.so                                                          
#4  0x00007ffff24fd5ae in IA__g_closure_invoke (closure=0x7fffdd7352b0, return_value=0x0, n_param_values=2, param_values=0x7fffc9909040,  
    invocation_hint=0x7fffffff9660) at /build/buildd/glib2.0-2.22.2/gobject/gclosure.c:767                                                
#5  0x00007ffff2512983 in signal_emit_unlocked_R (node=0x7ffff679f740, detail=<value optimized out>, instance=<value optimized out>,      
    emission_return=<value optimized out>, instance_and_params=<value optimized out>) at /build/buildd/glib2.0-2.22.2/gobject/gsignal.c:3247
#6  0x00007ffff2513d39 in IA__g_signal_emit_valist (instance=0x7ffff676a380, signal_id=<value optimized out>, detail=0,                     
    var_args=0x7fffffff9850) at /build/buildd/glib2.0-2.22.2/gobject/gsignal.c:2980                                                         
#7  0x00007ffff2514283 in IA__g_signal_emit (instance=0x7fffd0310a80, signal_id=24, detail=0)                                               
    at /build/buildd/glib2.0-2.22.2/gobject/gsignal.c:3037                                                                                  
#8  0x00007ffff10fd4a2 in gdk_display_close () from /usr/lib/libgdk-x11-2.0.so.0                                                            
#9  0x00007ffff4d0f1ac in MOZ_gdk_display_close (display=0x7ffff676a380) at nsAppRunner.cpp:2480                                            
#10 0x00007ffff4d13319 in XRE_main (argc=<value optimized out>, argv=<value optimized out>, aAppData=<value optimized out>)                 
    at nsAppRunner.cpp:3459                                                                                                                 
#11 0x000000000040271f in ?? ()                                                                                                             
#12 0x00007ffff6be3abd in __libc_start_main (main=<value optimized out>, argc=<value optimized out>, ubp_av=<value optimized out>,          
    init=<value optimized out>, fini=<value optimized out>, rtld_fini=<value optimized out>, stack_end=0x7fffffffe328) at libc-start.c:220
#13 0x0000000000401f99 in ?? ()
#14 0x00007fffffffe328 in ?? ()
#15 0x000000000000001c in ?? ()
#16 0x0000000000000001 in ?? ()
#17 0x00007fffffffe67a in ?? ()
#18 0x0000000000000000 in ?? ()
(gdb)