BetterPrivacy is a Firefox add-on that deletes a type of tracking cookie known as local shared objects (LSOs).
This type of cookie, known as 'super cookies' are particularly harmful because they store a huge amount of information and, crucially, can't be deleted like a normal cookie. BetterPrivacy finds the folder on your hard disk where the LSOs are stored and when you finish a session, deletes any it finds there.
It's fairly easy to configure BetterPrivacy, but if you don't want to change the settings, it works without configuration as some of the options are a bit complex. Under the Options section, you can choose exactly when the add-on removes LSOs, and configure it to keep certain LSOs if you so want. The BetterPrivacy help is very complete, so if you want more information on the process, you'll find it there.
Note that BetterPrivacy will wipe out any saved game data that you may have from playing games online so you must make sure that you exclude these from deletion in the preferences first.
BetterPrivacy is a superb tool to stop super cookies from tracking your internet surfing activity.
