BUG ID: Bugzilla Bug 16424 Enable auto-scroll in page by mouse middle click

STEPS TO TEST: For each iframe : Middle-click within the iframe and then move your mouse.

TEST PASS: For each iframe (except the 6th one which explicitly refuses scroll), you should see the scroll bars follow your moves and even reach the end of the page included in the iframe. You should also see an 4 arrow designed icon on the initial click location.

TEST FAIL: The scroll doesn't follow the mouse moves or doesn't get activated (except the 6th one which explicitly refuses scroll).