130 tabs?! Jesus. Just a few of those running active content like animated GIFs or Flash would account for the CPU. (Just because an app is minimized doesn't mean it can stop processing stuff. That model works for handhelds, but people expect their YouTube videos to keep playing anyway...) Never mind housekeeping on that much stuff. I'm not familiar with Firefox's internals, but I highly doubt they require plugins to be compiled against a profiler. They could, I suppose, but it's not trivial.

Sometimes I'm glad I grew up in an 8-bit world. It keeps me from driving systems to the point of failure just because I can.