Cookies can be removed on-demand and automatically based on pre-defined simple rules. Used to clean up cookies from certain sites or clean up all cookies except from certain sites. This can be done both on demand by a simple click or automatically.
Here is more information about this add-on from the developers:
This addon helps you remove cookies from certain hosts based on pre-selected preference. User has the option to either set preference to 1) remove all cookies except cookies from certain hosts 2) remove cookies only from certain specified hosts 3) remove all cookies. Once the preferences are set, user can apply this preference by normal left click on the cookie icon, added to the status bar. User’s selected preference is kept so that user has does not need to type in list of host names again and again. When you use firefox standard option to remove all cookies, you loose useful cookies that store your preferences and logged in sessions. With this addon you are in control of what you can delete or keep with one simple click. This is useful to periodically remove cookies from sites that put restriction based on information kept in cookies.
Want to learn more? You can pick up selectivecookiedelete from the Firefox Add-ons website.