The file toolkit/content/widgets/preferences.xml has dependencies
the first one being retrieved outside of try/catch lines and that breaks
XULrunner-based applications that don't have to use browser.* preferences.
(and this is undocumented... I'm going to add a warning in MDC).
These should move to toolkit.* and I'd love this to be fixed for next release,
hence raising flag.
Note added to MDC