That's not cpu use, that's ram use.
Something you need to consider, chrome has each tab in a separate process, and each of those processes takes up like, 60k average (depending on the page). Chrome eats ram just like FF does. Thing is, it's more secure, because each tab is a separate process, and all the other security measures they use. And on top of that, it takes up less CPU use (not ram) than FF does.
I don't have any exact numbers right now, but at some point, I'll do a comparison.
Also note, I use the developer builds. There's usually a huge difference between the dev builds and the stable releases.