The z-index of overlay and confirm are 100. When we plug USB in and make it as usb mass storage, the message will not be shown. It may be nice to move to original place.

BTW, there is a bug 897863 is related to it. The filmstrip and preview are also 100. So the overlay will not be displayed when filmstrip and preview are shown. I had made a patch for it which increases z-index of overlay to 110. But the patch of bug 897863 doesn't land. So, it is still nice to move to original place.