This seemed to be working before by a fluke:
> Before bug 1375870, _constructAfterChildren was getting called several times,
resulting in change events triggering updatePrivacyMicroControls repeatedly.
> updatePrivacyMicroControls was using the auto-private-browsing checkbox to
decide whether to disable and hide the checkmarks of the other checkboxes.
> After bug 1375870, at the point when updatePrivacyMicroControls is called,
the preference value has not yet propagated to the auto-private-browsing
checkbox, so uPMC doesn't work correctly and is not called again.
Solution: use the actual preference value in uPMC.
MozReview-Commit-ID: 2AhRQwkjH5Q
395ffdeb6f