I love this extension, but that the configs don't sync with my firefox account is a big problem.
Putting sites into appropriate containers is not trivial. Having to do this on every computer, or worse, losing your configs... is very discouraging.

The documentation encourages using it to manage multiple accounts on the same platform, however this usecase is not baked in. The default containers are not a bad suggestion. I used some of them. My custom containers centered around the third-party authentication and the specific account. So, I open youtube in a personal google account. I open google drive in a container for my work gsuite account.

Maybe some more guidance could be given on how to use containers. My big question is, does it make sense to separate websites that I authenticate with via twitter from websites I authenticate via facebook?

I think some built-in UX around organizing websites into containers based on specific authentication accounts could be a great feature.