Windows theme suddenly changed into classic and slows down

[GVincent]

So I was watching some youtube videos with mozilla and then all of the sudden the screen flashes, turns into classic theme, slows down my pc a bit (cpu usage suddenly >50%). This happened for like a minute and then everything back to normal again. This never happens to me before. Can anybody explain it to me? Am I the only one?

 

[Brink]

Hello Vincent,

I would say that is sounds like your WEI score may have updated at that time, or a video driver may have been installed through Windows Update.