Numerous browsers have a private mode to prevent local users from learning too much about your web habits, but what about preventing the sites themselves from tracking what you're doing? Mozilla thinks it can help. It just released a pre-beta version of Firefox whose updated, experimental Private Browsing mode blocks web elements that could track your behavior, such as analytic tools and social network services. While the measure could break some sites, Mozilla reckons that it's ultimately better to keep you off sites' radars by default. If you do run into problems, there's a central control area where you can tweak your privacy and security settings.