We should remove the per-OS implementations of nsIParentalControlsService in `/toolkit/components/parentalcontrols` and always use the stubbed-out `nsParentalControlsServiceDefault.cpp` implementation. When an implementation is present, URIs are sent to an `isAllowed(...` function that parental control software presumably can hook in the OS to filter content, and a `log(...)` method also takes in URIs.