This is how you can use any emoji as a favicon. I stumbled upon this code in one of my side projects, which is probably copied from somewhere else. I just wanted to post this here again, so that I don’t forget about it.

<link
  rel="icon"
  href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22>🙂</text></svg>"
/>