I solved it. Problem is next: gst-plugin-scanner run each times when start Iceweasel and take 100% core time When I killed this process in task manager browser work OK. https://bugs.launchpad.net/ubuntu/+sour ... ug/1286751
Browser sometimes freezes. And after close process one of core have 100% load. If repeat it (run browser then wait until it freezes) then next core have 100% load. Q: what is it? Q2: why freezes Browser?