I believe the videos tend to be playable on Microsoft Edge too.

Yeah last time I checked I couldn't play HLS videos in Firefox. Checking wikipedia it looks the same for Chrome but there are extensions available for both browsers.

It’s not like HLS is not an open standard; Firefox and Chrome just haven’t gotten around to supporting it for some reason. Edge supports it. I believe you can also drop the URL of the HLS manifest into VLC, if you prefer.

It's been a while since you checked, then; Apple's videos play anywhere now (including Chrome and Firefox). I think live streaming even worked in Chrome for 2019, which wasn't the case in some previous years (not sure about Firefox there).

That goes for everything on the Apple Developer Videos site, which goes back to WWDC 2014: https://developer.apple.com/videos/all-videos/

And you no longer have to send your registration in by fax! ;)