“Google Blog is reporting that Google is now faster on Firefox and Gecko-based browsers. Google has started using prefetching to start downloading top results even before the user clicks on them. This allows the user to view search results faster. Prefetching is not available on Internet Explorer and other non-mozilla browsers.”
Since the Prefetching can end up giving you cookies from sites you have not visited, they urge you to configure your Cookie settings in your Firefox options if it’s a problem. Read more at MozillaZine.