I've recently been having troubles playing videos on Firefox. My school website uses Vimeo embeds, but recently when I've put the videos in fullscreen, after 4-5 seconds it stops responding. The video freezes but the audio continues, and the controls don't come up when I move the mouse. I can press ESC to exit fullscreen, but the controls are still gone and the audio keeps playing. Then after a few more seconds I get the warning "This page is slowing down Firefox, to speed up your browser stop this page". If I don't use fullscreen but instead zoom in on the page, it also freezes. If I try the same things with Edge it does not freeze. I also made sure that it was only affecting Vimeo videos, by testing with other platforms and other vimeo links. I found previous reports of this issue, but all of them were either on Linux, or it was an issue with flash player, which is not relevant anymore. Not quite sure how to debug this but I would be happy to provide further info. It's really important that it works again :/ Thanks in advance! My repro steps: 1. Find a video on https://vimeo.com/watch 2. Play it and enter fullscreen 3. Wait around 6 seconds