This just recently started happening. If I start the tor firefox bundle, and log into Facebook the CPU usage goes to 100% and the computer slows to a crawl. If I stay on that page but minimize the browser the CPU usage goes back to normal, or if I simply open a new tab and go to that tab, it goes back to normal. This only seems to happen on Facebook. I dled the newest version and it does the same thing. But if I open FB on any of my non tor computers it is fine. I ran malwarebytes and it comes up clean.