Who's taking so much CPUs on Firefox!?

So Firefox always takes too much CPUs recently, just tried to figure out which pages really is heavier. and most suspicious pages was Google product... which I keep alive on any tabs usually.

For a way to measure that, just picked CPU load for a process up from top(1) command per 1 second within 1 minute randomly. and average it. Please note that there aren't actually any purposes nor solutions for this topic in this article. but this would be helpful to think about how to cool my laptop down to avoid a fan error as long as possible next time. because there seems to be an exhaust heat issue here.

Here is a result:

Page	Avg. CPU load
about:blank	1.31%
Gmail with Labs features	74.3%
Gmail without Labs features	65.2%
Google Reader	2.0%
Google Calendar	2.8%
Google Docs	3.2%
iGoogle with default content(Weather, Date & Time, YouTube and CNN.com)	4.0%

Well, I didn't do any operations during measuring this and may need more sampling in some cases so that it might relates to how often reloading in the background happens. to be fair, it's the fact that Gmail takes a lot of CPUs though.