I actually ended up using profiles (the way Chromium-based browsers do isolation) over containers. For my purposes it is nicer to have separate windows. For many sites I create a profile, then open that site in it, and "install as app" for even more convenience.

The only thing I used containers for was mixing personal and work stuff in one window.

Probably the best feature, imo, along with dev tools. I still use Brave and Safari Technology Preview on occasion, but reach for FF periodically because of the dev tools.