I'm not sure if the correlation is 100%, but you're right in that it will definitely work if "save image as" is available, and when it isn't, it'll be uncertain. I think there used to be code that looked for images more agressively so it would work more often, but then it started making virtually everything downloadable (page backgrounds, buttons, etc), which was horribly annoying too. 10/10 very fair review. :)

This addons works just fine and has the most important things it needs (and then some - I already find it too bloated compared to my original vision for it). I don't think it's fair of you to rate the addon itself lowly just because I don't implement all the non-essential extra fluff people open up request tickets on gitlab for. Ratings are supposed to indicate/be based on the quality of the addon as it is right now, not be used as a knife to put pressure on devs to add extra features you want. If it works fine for its intended use and has some extra bells and whistles, you can't justify 1 star.