In that case you can use multiple profiles.
Edit: Also IIRC multiple profiles cannot be synced across devices through the same firefox account while it is possible with containers
Containers are for being able to keep separate identities in the same browser window, but on a per-tab basis.
Profiles are for being able to separate different browser instances, with all their settings, extensions and so on.
While Profiles was used before to do the same thing that Containers now allow you to do, there are things you cannot do with Containers that you'll need to use Profiles for. Having separate extensions for different sessions is one of those things.