Xorg at 100%CPU when browser is on

[Yuri]

I saw this with firefox, now I see the same with chrome.

After a while when the browser is launched with ~10 tabs open, Xorg 
begins to consume 100% CPU and all graphics apps get sluggish. Quitting 
the browser brings situation back to normal.

It looks amazing to me that both firefox and chrome exhibit the same 
behavior.

Anybody sees the same? Anybody can explain why would such thing happen?

Yuri