I'm making an assumption as to what you are trying to accomplish; sorry if I "read" too much into your question or goals. The problem comes about when you try to log into multiple accounts that are on the same server. Cookies limit you to one session per server, so you need to log out of one account before trying to log into another account. This extension bypasses that limitation. https://addons.mozilla.org/en-US/firefox/addon/multifox/