I think the reason why it is so well integrated is that it used to be part of the standard installation of firefox and only later moved into an addon.
privacy.userContext.enabled to true
privacy.userContext.ui.enabled to true
privacy.userContext.longPressBehavior to 2
I love using containers with privacy.firstparty.isolate set to true too for extra protection.
I never understand why Mozilla doesn't allow to enable this in the settings.