When saving site as PWA with firefox, icon image does not appear

Describe the bug

After trying to install the app as a PWA, the image icon doesn't show up.

20201107_175512

Expected behavior There should be an image from the favicon showing up.

Smartphone (please complete the following information):

- Device: Galaxy A21s
 - OS: Android 10
 - Browser Firefox Beta 
 - Version 83.0.0

Additional context

Currently, we're keeping the site manifest in the favicon folder. Not sure if that's correct.
In the site.webmanifest file we have

{ "name": "Elm Quarto", "short_name": "Elm Quarto", "description": "Functional and accessible web app based on the popular (and highly entertaining) board game Quarto.", "icons": [ { "src": "/android-chrome-192x192.png", "sizes": "192x192", "type": "image/png" }, { "src": "/android-chrome-512x512.png", "sizes": "512x512", "type": "image/png" } ], "theme_color": "#000000", "background_color": "#ffffff", "display": "standalone" }


We only make mention of android-chrome. It may be necessary to add more to the icons list?

Any help would be appreciated on this.

**UPDATE**
[This web.dev article](articlehttps://web.dev/maskable-icon-audit/?utm_source=lighthouse&utm_medium=lr) seems to describe the problem. Apparently, the images in the icons may need a "purpose" field to enable that functionality. 

---

See [here](https://github.com/tkshill/Quarto/blob/main/README.md#run-and-install) in the read me for how to run and install the application.

See [here](https://github.com/tkshill/Quarto/blob/main/CONTRIBUTING.md#the-basics) in contributing for the basics on forking and cloning the repository.

tkshill / Quarto

When saving site as PWA with firefox, icon image does not appear #54