Firefox Nightly Container eliminate the need to sign out your first gmail or Facebook acct just to be able to sign in another account of yours, what if I tell you there's a way you can log in multiple accounts on the same site using one browser won't that be great?? Of course it would.
Thanks to Firefox Nightly, it helps you reduce the need to launch multiple browsers just because you needed to sign in your 3 Gmail account, with Firefox Nightly you can do all these on a single browser, it literally gives you the freedom to log in all your accounts on a site using your browser.
Firefox Nightly allows you to login up to four different account on a particular website and using just one browser. What this simply means is that, you can login your three gmail account (A, B, C and D) in the same browser window via container Tab feature. With this you can easily use multiple Facebook accounts without any difficulty.
How to use Firefox Nightly Container
Go to the File Menu (If you can't find your File Menu, just hit the alt key to access the File Menu) and select the “New Container Tab” option. Choose between Personal, Work, Shopping, and Banking.
Now, login your first account to Personal container Tab, then login your second account to Work container Tab, similarly log in your third account to Shopping and lastly you can log in your last account to Banking Container Tab.
Interestingly, all these three accounts can be used simultaneously at the same time without one obstructing the other. You can download the Nightly version of Firefox here