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.That isn't the only test underway. The pre-beta also enforces add-on verification by default, so that social plugin you downloaded shouldn't add unwanted toolbars, inject ads or collect more data than it should. Like with Chrome, you can turn off this filter if you're willing to throw caution to the wind. If you just have to try either of these features right away, you'll want to grab this early Firefox build now -- it's going to be a while before they make their way into a finished version.