Firefox Link Prefetching
I came across this article explaining how Google has started using link prefetching in an effort to speed up the search site. When using Firefox (or any other Mozilla browser), Google now prefetches the first result in the list. As they explain it, this means if you click on the first result that the page will come up faster because it has already begun downloading.
Mozilla has a Frequently Asked Questions document providing all of the details about link prefetching.