Comment 10 for bug 1898656

The snap with Firefox 84 has the same problem.

I tried Ubuntu Studio 20.04, that also uses XFCE and that worked fine and so do the Ubuntu 20.04, Ubuntu Mate 20.04 and Xubuntu 21.04 Dev.Ed.

However e.g Ubuntu 18.04 and Xubuntu 18.04 do have the same problem.

To be a little more precise. If you select the YouTube video by clicking on its thumbnail, it has that strange behaviour, if you click in e.g. the middle of the progress bar, the same problem repeats itself. The buffer builds up in both cases to say 60 seconds, while the screen remain static on say that first frame and then empties itself in a few milliseconds and that repeats itself many many times :)

However if you press the halt button in the left-down corner of the video and afterwards the play button, everything is working as expected. The same happens if you click in the middle of the screen twice as a start and stop action.

It only starts correctly, if you start it manually. The automatic start fails and so does the auto repositioning by clicking in the progress bar. I hope this helps.

There is probably some "timing issue" in the auto start, maybe forgetting that it should be displaying, because of a multi-threading/locking issue. In my experience this type of seemingly timing issues are often related to not locking shared data/buffers or locking it incorrectly.