Still the case.

The features is no used enought, people don't know about it, and because of that, there is no pressure to improve it.

E.G: the "forget this site" button will remove all cookies, local storage, cache, etc. for one site. Very handy, because I don't want to bust my entire cache every time. But it will remove them for all containers, which sometimes is not what you need.

Thanks. Ironically, this also means that chrome has more visible support for tab-containering, with its clear support for simultaneous windows with different profiles. Can I do the same in Firefox?

About:profiles is what you are looking for.

This is a messy workaround, but I just delete the container and create a new one with the same name.