One downside that I had hoped containers would fix was multiple accounts on AWS.
Because of the way AWS handles the URL's for logging in I get:
company1.signin.aws.amazon.com
company2.signin.aws.amazon.com
company3.signin.aws.amazon.com
BUT FF only seems to remember the login/password for 1 of these at a time. I had hoped that putting them all in different containers would fix this but it appears that FF only matches based on the base domain name, and not the full sub-domain.
If AWS had the domains structured as: AWS.com/company1
AWS.com/company2
AWS.com/company3
It might behave differently.