You probably have hardware acceleration enabled in the browser(or in flash, I'm not sure where that's set up) and that will use a chip on the GPU to decode the video instead of using the CPU hence the rise in temperature.
Approximately for a day but i can't log in for a days. When i wrote the last post i was logged in just for a one day. First i thought i was sign-out by server, that happened too but when i log-in into forum (i think forum and opera link are in common) i still can not see my Opera link bookmark.
p.s. i put stared (subscribe) i do not get e-mail for a new messages.