The idea is nice but unless this extension can sync all of your container settings to the Firefox account it's not worth the effort (I can do the same by creating a different profile), especially considering that it often forgets all your containers and you have to set them up from scratch (it's pretty frustrating).

Another missing feature is the ability to open bookmarks in a container quickly. There should be a context menu action for this, e.g. Right click a bookmark > Open in Container > Select a container.