Edge has a funny issue (in extensions at least) where it won't initiate an XHR to a URL that doesn't have a file extension. Eg, it will request https://example.com/list.txt, but fail when you try to request https://example.com/list.

It has nothing to do with whether the file exists or not; it fails when you try to send the request.

This may not be solvable in the extension and may instead require a fix on Edge's side.