The file toolkit/content/widgets/preferences.xml has dependencies to preferences browser.preferences.instantApply browser.preferences.animateFadeIn 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 https://developer.mozilla.org/En/XUL/Prefwindow