According to the MDN documentation, you should be able to use a different icon by specifying the icons property within the manifest.json file: https://developer.mozilla.org/en-US/docs/Web/Manifest/icons. Unluckily for us, this doesn't seem to work either. I'm currently playing around with the manifest and it's look like also other components are not behaving as expected, such as scope and display. Maybe further tests are needed.