Grayscale Tool

Press shift+g (or create your own key shortcut) to (de)activate grayscaling of a web page.

Originally intended for web designers who might want to test the contrast of their content by changing to grayscale, but this extension can really be used by anyone who for some reason want to remove the colors of a web page. The grayscale persists between page loads, and the key shortcut to activate can be customized in the options.