Please look at this URL

When I select any check box on left column then one pop up is display on screen.
This image shows properly in Fire fox. When I scroll up down then image is fixed in fire fox.
Vertically and Horizontal

But when I used IE and select check box on bottom left menu then I can't see pop up image.
Because this is not display vertically middle or it is not fixed.

Please give me idea or suggestion how I can fix it.