By accident, Dr Macenstein noticed that Using Safari can slow your system down as much as 76% vs Firefox, so he did some tests. And graphed them. He says:
The interesting thing about these results (to me at least) is that both Firefox and Safari were simply open during their tests. I was not actively "surfing", ie. clicking on things, moving windows, etc. It seems to me that a background application, especially one that should not really be doing anything all that processor-intensive even when in the foreground, should not hog system resources the way Safari apparently does. If Firefox can play nice, why not Safari?
Charles Arthur adds: Dave Hyatt, who leads the Safari team, responds on the Surfin' Safari blog:
One might expect that a background browser window would do nothing. However, that is a fairly naive assumption once you take a look at the kind of Web content that exists today. There are many ways in which a browser can still be doing required work even while in the background.
He mentions animated GIFs, plugins, Javascript timeouts and intervals, and so on. (I'd add adverts that auto-refresh, which chew up a lot of CPU.)
