This add-on adds buttons for managing site cookie permissions, switching global cookie permissions on and off, browsing cookies, and removing cookies. The same functions are included for local and session storage.
Here is a little more about the add-on from the developers:
You can use Cookie Controller solely from the tools menu, but most people will want to install one or more of the toolbar buttons. Open the customize toolbar palette by right clicking on a toolbar and you will find three buttons that you can drag onto a toolbar anywhere you like. You can choose plain buttons where context menus are accessed using a right click, or menu-buttons where there is a dropdown marker next to the button for accessing the menu.
You can pick up Cookie Controller from the Firefox Add-ons website.