This is a very good add-in, which lets me use Firefox for all my browsing and separating different uses from each other.
Previously I was using Ms Edge for work, but I don't need a separate browser anymore. And considering Ms is moving to Chromium, this is a very good time to switch totally to Firefox, if we want a free Internet.
It's also playing well with Facebook Containers. It just added another container for Facebook, without any effort on my side.