So that the safe mode dialog can remove the normal xulstore if necessary.

Better still, don't try to load or store anything in safe mode. (I don't know why this approach wasn't used for localstore which ironically was automatically switched to an in-memory data source during shutdown, unlike xulstore which just ignores writes.) I renamed init to load to make it clearer what's going on there. I conflated needsSaving and writeTimerInitialized as they have the same value. This allowed me to remove the now unnecessary callback function.