current TestFlight build (1104) iPhone 6 Plus (iOS 9.0.2) 1. Go to gmail.com 2. Scroll the page down slowly and observe the behaviour of the URL bar Result: The URL bar doesn't 'jump' into the hidden state. Instead, it overlaps the system bar https://www.youtube.com/watch?v=25ze9k7LXc0
It's hard to tell whether behaviour is incorrect. Safari does the same thing (it actually has a worse scrolling interaction than Firefox), and you can access the header by scrolling up. It could be that this was intentional on Google's part. We could change this behaviour to show the header by default if that seems like the right thing to do, though.
We should investigate and see if we can contact Google to see what's up.
The behaviour actually seems much more reasonable with the scrollbar changes introduced in https://bugzilla.mozilla.org/show_bug.cgi?id=1237694 Maybe this is actually acceptable now?