Yeah, I used to have the same issue with AWS because they kept your account in your session. Having containers for these things is much better than multiple profiles.
As you mentioned this, there is now a Firefox add-on that automatically creates the containers from the AWS SSO landing page as you click into your various accounts. It removes the need to create them manually with the Multi Account Containers add-on.
https://addons.mozilla.org/en-GB/firefox/addon/aws-sso-conta...