Firefox users exercise caution http://betanews.com/2015/08/15/firefox-stealthily-loads-webpages-when-you-hover-over-links-heres-how-to-stop-it/
This pre-fetching has been going on for years (not just in firefox) in the days of mass dial-up users, disabled by me. It used to be more than just hovering over a link that was prefetched. If you visited a page, you didn't even have to hover over a link, links in that page could be pre-fetched right away.
Check for '
prefetch' without the quotes in about:config and you will see and prefetch settings (including the old settings) depending on what add-ons that you have there may well be prefetch settings for those.
I think that mow we are in a mass broadband environment, you would think that pre-fetching would be dead and buried and not reinvigorated.