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. Google help adds that prefetching could end up with cookies from unvisited sites and provides Firefox settings to disable it.
News source: MozillaZine