I have a question and i can't find similar in other thread.
How can I log-in into Facebook or Yahoo or GMail or anything with two or more accounts in Firefox at the same time?
You can use this - CookiePie
It's an add on for FireFox that stores cookies for tabs/new windows separately from others. So, you can have one FireFox process running but have two tabs open, with both logged into a different Facebook account (or any other type of accounts you want to log into).
Hope this is what you're looking for!