There's no built-in feature along those lines. The closest thing would be a private window, but you need to close ALL private windows to empty the private window cookie jar; closing one tab won't destroy that tab's cookies. One extension which can destroy a site's cookies automatically when you close the last tab accessing that site is: https://addons.mozilla.org/firefox/addon/self-destructing-cookies/ Note: You still should expressly log out of sites when you are done with them. Otherwise, your session may remain open indefinitely.