Remember back in the day when google images used to have "All sizes" (or "More sizes") link right under the image you are viewing?
Well, this script does just that.
Notes:
Make sure to allow pop-ups when prompted.
Make sure to allow requests to all domains when prompted.
Make sure you are on the '.com' domain extension.
'Full Size' button will simply open the preview image in a new tab. it does not force loading the full size image.
Keep in mind that "All Sizes" button is not perfect. E.g., in some cases it does not find anything, and the picture you are viewing might not be among the results. But that's just Google for you. Can't do anything about that xD
