Shows a lot of promise, but it has a ways to go to replace the Save Images addon: https://addons.mozilla.org/en-US/firefox/addon/save-images/

For galleries, would it be possible for the addon to follow the thumbnail links and then download the full sized images there (assuming they're the largest resolution images at each link destination)?

Example: https://www.artstation.com/vaughanling

Alternatively, if each of the thumbnail links were opened in a new tab, could the addon be made to download the largest image in each tab?