The Firefox documentation says to Enable Containers through General Settings -> Tabs [1] but there is no such checkbox [2]. Going into about:config and changing privacy.userContext.enabled and privacy.userContext.ui.enabled to true [3] enables the checkbox in the settings page [4]. This is Firefox Version 116.0.3 under Ubuntu.

I use Chrome and Firefox interchangeably so I don't have a dog in this fight. Containers aka Personalities needs to be made a first class feature in Firefox and not require the above steps to make it useful to the less tech savy end user.

1. https://support.mozilla.org/en-US/kb/how-use-firefox-contain... 2. https://imgur.com/a/mX1P25J 3. https://imgur.com/a/fNyRnLk 4. https://imgur.com/a/GjxJwIP