not sure what, if anything, can be done about this, but there's an @unexec in xulrunner which runs the old (pre-upgrade) xulrunner to unregister things which fails..
xulrunner-1.9.2.28p6 (deleting)| | 0% (process:12242): GLib-GObject-CRITICAL **: gtype.c:2720: You forgot to call g_type_init() (process:12242): GLib-GObject-CRITICAL **: gtype.c:2603: You forgot to call g_type_init() ** GLib-GObject:ERROR:gvaluetypes.c:457:_g_value_types_init: assertion failed: (type == G_TYPE_CHAR) Abort trap (core dumped) system(/bin/sh, -c, xulrunner1.9 --unregister-global) failed: exit(134) xulrunner-1.9.2.28p6 (installing)|****************************************|100%Warning: Configuration file '/etc/gre.d/1.9.2.28.conf' already exists. No action was performed. system(/bin/sh, -c, xulrunner1.9 --register-global) failed: exit(2) xulrunner-1.9.2.28p6->1.9.2.28p6: ok