It is a preconfigured generic container that has a few extra settings to further isolate Facebook specifically, as it is so insidious in its reach around the web.

The user 283894 makes a point that sometimes, it's nice to have your logged in Facebook container separate from other Facebook content.

Firefox has Containers generically, this extension just applies Containers specifically to Facebook

If you use the normal Containers addon, you can be logged in to a different FB account in each Container. With the Facebook Container, all traffic to FB is blocked outside of the Facebook Container, and any attempt to navigate to Facebook will be hijacked into the Facebook Container.

There is also a special Google Container which works similarly.

"Facebook Container" is just a simplified version of https://addons.mozilla.org/en-US/firefox/addon/multi-account... (both are made by Mozilla).

Mozilla made an extension specifically for Facebook.

A nuclear waste bin is a specialized kind of waste bin