We released Tor Browser 10 this week which is based on Firefox 78 ESR and since then a lot of users reported that Youtube videos on Windows don't play anymore. One only sees an error message: "An error occurred. Please try again later (Playback ID: $ID) Learn More"
This is not a Tor Browser-only issue, though, but happens with regular Firefox 78 ESR, too, as long as they are built with mingw-clang. I could not test nightly builds as I only get a white screen, so this is busted differently. The debug build did not have any useful info in the console as far as I could tell.
So folks saw in Tor Browser something like
Media resource blob:https://www.youtube.com/754495fa-09d2-4478-8bfc-02b7d64d19a4 could not be decoded. watch
This error message will be blank when privacy.resistFingerprinting = true. If it is really necessary, please add it to the whitelist in MediaError::GetMessage: NS_ERROR_DOM_MEDIA_FATAL_ERR (0x806e0005) - mozilla::MediaResult mozilla::RemoteAudioDecoderChild::InitIPDL(const mozilla::AudioInfo &, const CreateDecoderParams::OptionSet &): RemoteDecoderManager is not available. base.js:6004:19
in the browser console which might give a hint about what is going on.
Users reported that flipping
media.rdd-opus.enabled back to
false "solves" this problem.