That is weird indeed. It’s good for me, I get normal playback. Maybe try a different browser? Or maybe try to nudge it a little, click forward on the video and see if that jumps it into working.
Probably just a Browser Cache thing; last time I tried it, I also just got an infinite loading ‘circle’, but since then I went back to ‘Clearing Cookies and Site Data every time I close Firefox’ and now it plays just fine.