One of the most STUPID and annoying creations by Mozilla/Firefox is prefetching. IMHO, one day because of this idiotic feature, Firefox may end up being banned by most webmasters. Unless, M$ stupid enough to follow the mistakes of Mozilla.
A browser (firefox) with prefetching option ON or with Goolge accelerator/prefetcher will download every links founded on your site. It behaves exactly like a bad/rogue crawler trying to crawl every links of your site.