Back in like 2017? or 2018 when Containers came out for Firefox, I used the Multi-Account Containers Extension to manage QA testing of web apps, I'd have a container labeled for the user I wanted to log in as and test. It's insanely useful for the web.

What's also interesting is Tor Browser could probably take full advantage of containers later on, but I'm not sure if they would come up with a specific way of using it or just disable it.