I'd love to see you try serving the exact same file for both but the trick is that you need to return different Content-Type headers depending on what is reques

I'd love to see you try serving the exact same file for both but the trick is that you need to return different Content-Type headers depending on what is requested. When the browser requests /favicon from a navigation event it will use Accept: text/html etc, you return the file with Content-Type: text/html and inside the response you have a <link rel="favicon" href="/favicon" type="img/png"> literally the same resource but the browser will now likely fetch with Accept: image/... and you could return the same file with Content-Type: image/png and the same resource will get used for both. Unless the browser caches the response, I feel like this would work. If you don't control the headers of your webserver (eg GitHub Pages) I would settle for a symlink favicon.png that just links back to favicon.html which I think would trick the server into returning different Content-Types.