This add-on is not, and doesn't intend to be, a replacement for the official Mozilla Multi-Account Containers add-on, which is the tool you should be using to manage your Firefox containers. Switch Container will never be a container manager, as that would be out of the scope of what the add-on was made for, and would bring bloat to a piece of software intended to only do exactly what it says on the tin, nothing more, nothing less. It's therefore recommended that you install and use the Multi-Account Container add-on by Mozilla for container management.