Except for the new era IE browser Safari, most other browsers basically support using SVG data URLs for icons, so you can directly use the text form of SVG to input emoji symbols.
<link
rel="icon"
type="image/svg+xml"
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>"
/>
Replace 😊 with any emoji symbol and place it inside the <head>
tag.