Using FF 72.0 & Multi-Account Containers 6.1.1 looks like this kills M-A Containers. Checked this several times and isolated the problem to …
In Privacy & Security -> History >> change it from default to “Never Remember History” it also breaks Multi-Account Containers. It still exists in the active add-on list but doesn’t work and disappears from the menu and mouse selection. To get it back I have to Restart with Add-ons Disabled -> Refresh FireFox -> Add-on Manager > Containers reappears as working add-on but any customization is gone.