The latest version of the Firefox Web browser, 5.0, offers numerous reasons to upgrade. One of the major changes is the ability to enable the Do Not Track feature. This feature lets you tell a site that you want to opt-out of third-party tracking for behavioral advertising. In Firefox 4 this feature was buried deep in the options -- Options >> Advanced >> General and under Browsing you'd check the option: Tell web sites I do not want to be tracked. Now you just need to go into Firefox Options >> Privacy and under Tracking check Tell web sites I do not want to be tracked.
Firefox 5.0: 5 Reasons To Upgrade