It seems we were both wrong. Forhackernews was most likely referring to the new web app system. Websites that register themselves as web apps get their own launcher icons, run in their own window, show desktop notifications, etc., and they're powered by Ubuntu's custom QML-based browser which is referred to as Ubuntu Browser.
Firefox is still there, and still branded as Firefox. Ubuntu Browser isn't intended to replace it outright.
Debian upstream does the same thing. Mozilla doesn't allow use of the Firefox trademark for non-Mozilla builds.
http://en.wikipedia.org/wiki/Ice_Weasel