The article links to https://support.mozilla.org/en-US/kb/profile-management. From my memory of how profiles worked previously it's mostly a fresh coat of paint for things you could do before.

The two most exciting things to me:

1. You can now launch and manage profiles from a menu hidden in the account menu (feels like the wrong place to put it, but shows up for me even though I'm not signed in)

2. Mozilla actually cares about profiles again. The feature felt mostly abandoned before, nearly inaccessible without command line flags or the very bare-bones and ugly about:profiles