I think people forgot that Firefox is no meant to be a media player, but a browser, if you want to have a video player with fancy features, then use an adequate video player like VLC or similar.
@FairplexVLC or other standalone media players dont support the VSR either, only browsers that use Chromium have it... So firefox will have to implement it separately since it doesnt use chromium
+ Media players cant play LQ videos on the internet... for which the vsr is especially made