HTML5 Playback causes choppy scrolling

Question

HTML5 videos cause choppy scrolling - most notable when playing a YouTube video in a tab, and browsing in another one. If the video is paused there is no problem. Also, which is a bit weird, if I click on a YouTube video, and before it manages to fully load, switch to another tab, the scrolling is fine. If I switch back to the YouTube tab, it immediately gets choppy in all of Firefox. Similar problem with 9GAG gifs for example, so it's not just with YouTube.
All drivers are up to date. Windows 7 Professional N, hardware acceleration on or off makes no difference. Any ideas?

Answer 1

Also good to mention that if I switch to YouTube flash, the problem is gone, however Flash gives such a sh** performance, that I would rather tolerate a bit of choppy scroll than using the flash player :)
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