It sets up the Facebook container so you'll automatically switch to it whenever you go to Facebook. If you checked "Always open in Facebook" in the containers dropdown while on facebook.com, then checked "Remember my decision for this site" before clicking "Open in Facebook container" when opening facebook in a different container, it's the same.
The extension also cleans up Facebook cookies from your other containers. This extension is what got me using containers, but I deleted it after I realized it doesn't do anything after the initial installation.
Edit: Apparently this extension also prevents you from opening other sites in the Facebook container.
The extension also cleans up Facebook cookies from your other containers. This extension is what got me using containers, but I deleted it after I realized it doesn't do anything after the initial installation.
Edit: Apparently this extension also prevents you from opening other sites in the Facebook container.