It has been enabled by default for multiple years, time to remove it.

I think we may still need/want this as an emergency off switch because of the security and privacy characteristics of the API. (That said, sometimes prefs like this aren't actually implemented in a way that works as an emergency off switch, but instead as a "no new things" switch. However, that can still be valuable if there are potential attacks in the wild which would inherently depend on new uses of an API.)

Makes sense. I'll restore it in https://phabricator.services.mozilla.com/D150441 in that case. Closing for now.