Facebook Container add-on conflicts with Multi-Account Containers add-on. when I open Facebook.com in a container I made it reverts back to "Facebook Container" Container.

If you manages two Facebook accounts, one without container (AKA with Facebook Container) and another with a container made with Multi-account Containers, then when you open tab in that container made with Multi-account Containers, and navigate to Facebook.com it will open Facebook.com in the Facebook Container add-on.