Cookies are small files used to identify your state or behavior, of your last browsing session on a particular website. Cookies are automatically downloaded from the website you browse and can be used to retrieve data relating the user’s previous activity, such as security information, navigation styles etc.
The most desirable thing a user can do is, destroy cookies when we don’t want them to be used. Self-destructing cookies is a Firefox add-on that destroy cookies that no longer used by an open browsing session.
When installed, it can monitor cookies that are tracking your activities, and destroys it after certain period of time (10 sec default). Automatically cleans your cache every time you are not actively using the browser thereby minimizing security risks caused by unwanted cookies.