You will need to install a user script manager extension to install this script.
In the name of not performing destructive transformations on captured information, DOS emulators generally don't correct for how old DOS games running at 320x200 used non-sqaure pixels.
This wouldn't be a problem on its own, except that MobyGames also presents screenshots unaltered, so screenshots appear vertically squashed compared to how they would appear on a real CRT.
This script implements the best algorithm for screen display suggested in this Gamasutra article so that, with a single click, you can enable aspect ratio correction on any MobyGames screenshot with a resolution of 320x200.
(Note that, because part of the aspect ratio correction is performed live in the browser using CSS, saving the aspect-corrected screenshots won't give you what you expect.)