When Firefox identifies a website, it automatically starts Pre-loading all the links contained in it in the background. Since you seldom surf further in the sites, you prefer to remove this system brake and do without this 'Service'?
Here is the trick :
Change a function in the advanced configuration before deactivating the Pre-fetching function. Type "about:config" without quotes in the address bar and press Enter. Look for the "Network.prefetch-next" entry in the list. Then right click on it and select the context command "Switch". Check Whether the Boolean Value is set to "false". In future, your system will download the websites only when you click on a link.
The Anticipatory downloading of linked sites is known as Pre-fetching. This function is supposed to speed up the downloading of a site when you click on a link. However, since you would hardly visit all the links in a site, this function is generally of no use. To top it, Pre-fetching brings load on the bandwidth, contributes to high data quantities and costs in the volume tariff, causing the browser cache to fill quickly and demand high storage requirements in system RAM. These disadvantages outdo the advantage-the speedy downloading of a site, it is therefore which more advisable to deactivate this function.