Sorry, the main process goes to 140%, and about 5 more other firefox processes start chewing up 80% cpu each. I just added them altogether.

I have seen it spike to 400% a few times in activity monitor.

As to what I'm doing, open up say lobsters, click on all the tabs that look interesting, forget them for a day, repeat. End of the week have a look see at things.

Mac shows CPU usage as 100% per core. Means he has a quad-core or dual-core w/ hyperthreading.

Linux does the same thing too. I wonder whether this is a POSIX thing, or if it's just a rather common UNIX thing.