Comment 16 for bug 1775719

I push-squashed another commit to address the Download button not getting disabled, but not exactly how you might expect. If the download fails outright, the button should be re-enabled, but that bit was only partially working, which lead you down this path in the first place.

If you confirm a file exists (see my previous comment), then I can add more debugging to the file retrieval code. As it stands, it looks like the file's not accessible to the browser (i.e. does not return HTTP 200).