You can use containers for any website / group of webistes.
The specific Facebook-only container extension is for people who don't want to hassle of organizing their containers themselves and only want one for Facebook.
You can accomplish it without any extension by creating a 'Google' container and choosing yes on every Google site when it asks you if you want to always open in that container.
Or you can fork the extension, change the container name and color, and update the array of domains.
The specific Facebook-only container extension is for people who don't want to hassle of organizing their containers themselves and only want one for Facebook.