On: Apple Events – WWDC Keynote, June 2017 [video]

[avaer]

Also latest Chrome.

Few companies could get away with this UX, but Apple is one of them.

[derefr → avaer]

HLS is an open standard (and a very simple one); Firefox and Chrome have just avoided implementing it for some reason.

[avaer → derefr]

From my reading, it appears off of any standards track it might have had -- it remains something Apple made up and can change however they like.

Which would be a great reason for not implementing it in an open browser.