Gran Paradiso "the latest version of Firefox” is nearing release. Gran Paradiso includes a form of malware protection that checks every URL against a known list of sites. It does so by sending each URL to Google. In other words, if people enable this feature, they get some malware protection, and Google gets a wealth of information about which sites are popular (or, for that matter, which sites should be checked for malware). Fair deal? Not to worry ”the feature is disabled by default."

http://www.mozilla.org/projects/firefox/3.0a8/releasenotes/