The technology is meant to address one of the older privacy problems on the Web, namely the fact that Web sites can see which links a user has visited. The developers at Mozilla soon will be adding a new privacy enhancement to the Firefox browser that will help prevent attackers and the operators of third-party Web sites from seeing which other sites a user is visiting. The changes are under-the-covers type modifications that should not make much of a difference in the way that users view the sites.
Source: https://threatpost.com/mozilla-fix-css-history-leak-soon-033110/73763/