The developers of the Facebook Container extension changed the underline colour from blue to black instead. Facebook Container should still be working as expected.

As long as there is an underline of some colour under the tab, it shows that Facebook Container is working properly. You can have more than one Facebook Container tab open, which is why logging out of the 2nd tab will also log you out of the 1st.

Oh maybe have I misunderstood the usage of container tab? I thought that if I open the 2nd facebook tab, I can log into another account at the same time. Is my understanding wrong? Thanks very much

Actually, perhaps I have misunderstood your question. Are you referring to the Facebook Container or the generic Multi-Account Containers?

Yes, I had same questions.

So tabs do maintain login data consistency in such a way that once logged it, next same tab (e.g Facebook Container tab or Work Container tab) will offer same account.

I guess it works in similar way with all other "Work, Personal, Banking and Shopping" tabs also!'

That's correct MinäJaHän. Basically, each container is similar to if you were to run multiple versions of Firefox. It just eliminates the hassle of having to do that.

A common example would be email. You can login to your personal email in the "Personal" container and then login to your work email in the "Work" container. The account that you are logged into will be contained to each tab.