In the latest Facebook Developer’s blog, Facebook announces that
Platform dialogs are all built to run in a variety of display contexts on both the desktop and mobile web. As part of our continued efforts to make these dialogs work smoothly in all contexts, dialogs, such as Feed Dialog, Pay Dialog and Auth Dialog, will now open inline by default as a modal overlay for Canvas and Page Tab apps. These dialogs provide a better user experience than previous pop-up dialogs and do not require the user to turn off pop-up blockers. For more information, please see our documentation.
Other than having the possibility of opening the Auth Dialog as a modal overlay, I think the major benefit of making this move is that we now have a more consistent way of displaying the platform dialogs instead of seeing modal overlay in some cases but pop-up dialogs in some other cases.
Thanks Facebook team for bring me feature to us.