Update on the iPhone using Firefox:
I tried it again with the same results but then I found the option to use the desktop site and it showed up. But there were still oddities.
I tapped to play the video but when I’d click the x to exit the video window, it would start the video again in about a second. Same if I tapped to pause - it would quickly resume playing.
Then I switched back to the mobile site and it was suddenly working. And no problem with the video. Checked the desktop version again and had the video problem.
No idea if this has been the case in the past on the iPhone as I never tested it before.