The Firefox Multi-Account Containers is a more general extension that allows you to create containers and determine which sites open in each container. This extension can be customized to suit your needs for multiple sites and multiple logins but takes more time to set up than Google Container.

I think this one also makes sure that links you click inside the Google container get opened outside of it?

It serves different purpose. These Facebook/Google containers are for automatic isolation. The Multi-Account Containers is for creating and managing containers.

I've been using MAC for a week, and just added this extension. It immediately shows up in the MAC as an option. SO (I assume) it's no better than just creating a MAC 'google' container. Just easier.

I'd been using a 'sketchy' container for YTube, but dropped YTube into this. Thereby isolating (I think) YTube from the other 'sketchy' sites I may visit. As for Google ... long-ago blocked it and FB on the network level. Chopping off -some- of the octopus' tentacles.