If I wanted to completely separate things like this I would use multiple different profiles. The advantage of the extension is that your history, settings, etc remains constant across the containers.
Profiles are unfortunately much more cumbersome to use than in Chrome.
The UX that container tabs have - being able to use them in the same Windows as other tabs, with accessible open-in options from the tab bar and from various context menus; creating new containers as easily as specifying a name and no more - is the UX that I wish Firefox had for their profiles.
