" ... While it is in theory an interesting concept to speed things up for the user, critics argue that it is creating unnecessary overhead and that it has privacy implications. Resources that are prefetched but not accessed are wasted for instance as they remain unused. As far as privacy is concerned, the server the information are retrieved from notices the user's connection even if it is caused by the automated process. ...Source: Ghacks.net
"Firefox users can disable this prefetch feature the following way: ..."
Address : Firefox prefetching: what you need to know