Tampermonkey script to update Favicon with data-uri SVG for Chrome 80+ etc

TampermonkeyFavicon.js

// ==UserScript==
// @name         SVG Favicon test
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Update the favicon on a site
// @author       You
// @match        https://elliz.github.io/svg-favicon/
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // play with https://codepen.io/elliz/full/ygvgay for getting it right
    // viewBox is required but does not need to be 16x16
    const svg = `
    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
      <circle cx="8" cy="8" r="7.2" fill="gold" stroke="#000" stroke-width="1" />
      <circle cx="8" cy="8" r="3.1" fill="#fff" stroke="#000" stroke-width="1" />
    </svg>
    `;

    var favicon_link_html = document.createElement('link');
    favicon_link_html.rel = 'icon';
    favicon_link_html.href = svgToDataUri(svg);
    favicon_link_html.type = 'image/svg+xml';

    try {
        let favicons = document.querySelectorAll('link[rel~="icon"]');
        favicons.forEach(function(favicon) {
            favicon.parentNode.removeChild(favicon);
        });

        const head = document.getElementsByTagName('head')[0];
        head.insertBefore( favicon_link_html, head.firstChild );
    }
    catch(e) { }

    // functions -------------------------------
    function escapeRegExp(str) {
        return str.replace(/([.*+?^=!:${}()|\[\]\/\\])/g, "\\$1");
    }

    function replaceAll(str, find, replace) {
        return str.replace(new RegExp(escapeRegExp(find), 'g'), replace);
    }

    function svgToDataUri(svg) {
        var encoded = svg.replace(/\s+/g, " ")
        encoded = replaceAll(encoded, "%", "%25");
        encoded = replaceAll(encoded, "> <", "><"); // normalise spaces elements
        encoded = replaceAll(encoded, "; }", ";}"); // normalise spaces css
        encoded = replaceAll(encoded, "<", "%3c");
        encoded = replaceAll(encoded, ">", "%3e");
        encoded = replaceAll(encoded, "\"", "'"); // normalise quotes ... possible issues with quotes in <text>
        encoded = replaceAll(encoded, "#", "%23"); // needed for ie and firefox
        encoded = replaceAll(encoded, "{", "%7b");
        encoded = replaceAll(encoded, "}", "%7d");
        encoded = replaceAll(encoded, "|", "%7c");
        encoded = replaceAll(encoded, "^", "%5e");
        encoded = replaceAll(encoded, "`", "%60");
        encoded = replaceAll(encoded, "@", "%40");
        var dataUri = 'data:image/svg+xml;charset=UTF-8,' + encoded.trim();
        return dataUri;
    }

})();