https://addons.mozilla.org/de/firefox/addon/temporary-containers
The addon uses Firefoxes containers best, they are auto deleted after usage, quickly opened via the button, assigned to URLs and much more. This has to be integrated, to have people actually use the containers.
At the moment there is only private mode, Temporary containers replaces that too, allowing to autodelete every content of tabs in the containers, but with multiple environments in one window and easy closing and opening.