Firefox - how do I log in onto multiple (for example) gmail accounts?

Hey all
I need a way to login on multiple for example gmail accounts/facebook accounts etc, on my firefox, new firefox window still shares everything, if I log out on one, all log out.
I tried installing firefox twice in two discs, doesn't solve the problem, going private-mode doesn't solve the problem either.

 

I'd love for a way for this to work for chrome too, as my hotmail account uses a different login than my my xbox gamertags, and it would be nice to be able to have both logged in simultaneously. Hit me up with a PM if you find a solution

 

Just use two different browsers.

 

Doesn't help if you want to be able to have a fair few accounts logged in simultaneously. Nobody wants more than three browsers installed at any given time either.