Edit again: the auto focus-switching thing seems to be fixed :)
Edit: Okay I found that Firefox Multi-Account Containers extension and that's pretty much exactly what I was looking for so... :D
Fantastic. I would love a 'generic' implementation of this for any arbitrary site! Though I don't know what specifically goes into containing any single website in terms of maintenance when that website updates or uses unexpected content networks/resources and that sort of thing...
My biggest complaint is that it should not automatically switch focus to the FB page when I open FB in a tab. If not for that, 5 stars.

Great plugin. If you love this plugin, consider getting the Multi-Account Containers extension to use with all the sites you visit: https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/

Super, konečně se rozhodl někdo postavit facebooku. Jen tak dál ! Moc děkuji :)) super doplněk.

1a Aktion von Firefox, Addon funktioniert klasse

Excellent. Should be part of Firefox by default.

Stops facebook from spying on you when you're browsing internet. Thanks Mozilla team.