The primary browser navigational UI should now behave as if it's connected to
the page content in the viewport, including things like:
* Content page's URL is displayed in location bar
* Content page's title is displayed on the tab
* Back / forward navigates the viewport
* Entering a location navigates the viewport
* Page loading progress is displayed in the status bar as usual
MozReview-Commit-ID: FzxWEwj13sJ