We all know that 2 G-mail/Google accounts can be used in a single browser at a time, but how many of us know that the same can be done with FB account.. really very few..
Give a try, it's very simple.
All you have to do is open 2 tabs, one with "www.facebook.com" and another with "www.v6.facebook.com" enter two different user accounts and see the result for your self..
Here is a demo video for you..!