1) Visit this URL, let it play for 22 seconds, listen to your laptop/desktop CPU fan start screaming. Espected behavior: the video should loop. Actual behaviour: the video hangs just before the end and CPU usage goes to maximum 2) While the video is hung, close the tab. Expected behaviour: the tab and all its resources should be freed, which should stop the high CPU usage. Actual behaviour: the tab closes but CPU usage remains at maximum. 3) Shut down the browser and restart. Expected behaviour: The browser should close, and then the browser should start when clicking the app icon again. Actual behaviour: Firefox closes the window but remains at max CPU usage indefinitely. Firefox is unable to restart. Here's the URL which causes the problems listed above: http://ukcom.org/l/h/miwflow330px.html