I did a test on a video page I watched a couple of weeks ago on my laptop with no problem.
http://64.27.176.201/earthday/
First on Shiira, the CPU spiked almost immediately to 60% and the browser crashed.
OW did the same but did not crash and when I closed the page things went down to normal, which is much better naturally.
So I see what you mean about the sites causing something like this to happen. However, the result was not exactly what I'm talking about. First it wouldn't have seized the CPU immediately but over time; and second it wouldn't have let go of the CPU when I closed the page or even the browser, but only on restarting the machine.