It is an extension for Firefox, but one created by Mozilla. It's official in that sense, but it does seem a little strange it's not included by default. https:

It is an extension for Firefox, but one created by Mozilla. It's official in that sense, but it does seem a little strange it's not included by default. https://addons.mozilla.org/firefox/addon/multi-account-containers/ https://addons.mozilla.org/firefox/addon/multi-account-conta...