Multi Resolution Preview
I Recently presented a slide on a projector whose resolution was very low, and it messed up the iframe link I had in the background. This could have been averted using some sort of multi screen resolution viewer that highlights incompatibility risks. This could work as a test we could run in the slides menu.
Paul M. Walker commented
An extension for developers to test web pages in different screen resolutions ... to preview their websites in different screen resolutions.