After the November update I had to reinstall the Media Feature Pack (KB3010081) in order for Firefox to use YouTube and Groove Music to work correctly. After a successful installation, neither work. YouTube only shows 360p with no H.264 encoding and Groove Music says I am suppose to install the Feature Media Pack.
I already tried a Systemrestore and reinstalled the update but still no luck. It seems I am not the only one with this problem. Is this a Windows 10 N November Update bug?