When you use Firefox browser in conjuction with Google search engine, Google will prefetch the first page of the results. This means the first result page and the cookies associated will be downloaded to your computer even though you never click the link. If you do not want prefetch function, you can disable it by:
2) Type about:config in the address bar and press Enter
3) Scroll down the resulting preference list to network.prefetch-next
4) Double click network.prefetch-next so the value is set to false.
5) Close Firefox and restart it to enable the change.
Source: About.com article by Mary Landesman