How to limit the viewing area when viewing fullscreen?

Hello.  When I playback swfs they run fine until I view them at full screen.  At that point I can see all the unwanted 'scratchpad' stuff to the right and left of the stage.  How do I constrain this?  Do I need to address this in the original fla files?  Ideally I would like the sides of the screen (non-stage area) to be black.

Thanks a zillion!