Mozilla is getting a lot of hate lately. And it's understandable, and I wish they were better too.
But I have been loving the ease with with I can be logged into the same websites under multiple accounts, and firewall Facebook from the rest of my everything, and manage cookie-sessions in general since I installed this plugin a moon or two ago.
I still love #mozilla and I don't think there's a more free browser which I can actually use.
https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/