So, after a bit of testing with the example from the super-fetch-plugin, I’ve tried different kinds of websites and it worked, including a URL from comments-plugin.perchance.org, which I got from inspecting a comments plugin iframe from the DevTools. But in this case, not from user-uploads.perchance.org, it kept having the same CORS issues just like the ordinary fetch function. Specifically I wanted to get a text content from a file mentioned in the huge-emoji-list pack.

I think it’s a very neat concept when we could “superfetch” a content uploaded from https://perchance.org/upload right from any generator, but at least, that’s I’m getting for now.