The Windows parental controls API (e.g. IWindowsParentalControls) appears to
have been removed entirely from at least more recent builds of Windows 10. The
interfaces are still defined, but at runtime creating instances of them fails.
This patch enables us to tell if web filtering is enabled for the current user
on Windows 10 without going through that API by directly reading the relevant
All methods of nsIParentalControlsService other than parentalControlsEnabled
have been left unimplemented because it isn't obvious how to implement them
in this environment, since no replacement for the old API seems to have been
provided. For example, it appears that loggingEnabled could be implemented
using the same registry key, but the logging mechanism is unlikely to be
compatible with the old one, so reporting that it is enabled may be unsafe.