I always open Process Explorer (free) to see what's taking up the CPU, and kill it or at least suspend it to find out if that helps.
Had FireFox do that several times.....up to 90% CPU, had to close it all down and re-open it.
FaceBook seems to be the worst culprit, slowing it all down, followed closely by ANY Yahoo group. I do believe they are mining for data, and when they run up against Ghostery, ABP, and such on my confuser, they loop.
I'd rather have that than let Zook have at my data.