While this seemingly works, unless I'm mistaken, the top-level tabs demonstrated in the video load the destination URL into the framed area below *without scrollbars* (horizontal or vertical), making it largely useless!
The top-level tabs are seemingly meant to load URL's that provide their own scrollbars (e.g. as built-in tabs currently do).
Adding a top-level tab seems awfully useful, however. Can this scrollbar issue be addressed in a hotfix?