Ghostery is an excellent Firefox add-on designed to prevent sites from tracking your activity on the net. These include trackers, web bugs, pixels, and beacons placed on web pages by Facebook, Google Analytics, and over 400 other ad networks.
Ghostery only blocks once it has alerted you to what sites sites are trying to do. This includes revealing the identity of trackers and even their script source. Ghostery can be managed and monitored in the Firefox taskbar. By right-clicking the little ghost icon, you get access to Help (online), Options (not many) and information on the trackers.
When Ghostery does not detect any bugs, it is gray, and when it sees something watching you, it turns red and highlights what it has found, displaying a warning in the taskbar and a small floating square containing the names of the bugs and trackers on the website in question.
Ghostery also offers you the option of collaborating with other Ghostery users to make it more effective. This is done via a feature known as GhostRank, which sends Ghostery servers anonymous information about the trackers you encounter and where you encounter them helping the developers to create a comprehensive list of detectable items. However, the developers assure that Ghostery places no cookies in your browser, there's no sign-up required and there's no tracking of your internet usage.
Ghostery is very efficient to the point where you may find it a bit intrusive at times. It may also cause crashes when certain objects try to launch in Firefox.
Overall though, Ghostery is an excellent Firefox add-on for those that want to take control of their surfing privacy.