On https://github.com/mozilla/pdf.js/wiki/Required-Browser-Features we mention required browser features for PDF.js, but I have the feeling that not all of them are necessary nowadays since we moved to using more modern features over the years. Moreover, as indicated in https://github.com/mozilla/pdf.js/issues/11950#issuecomment-637149085, some features may be missing such as range requests or `async/await`.

In short, we should verify which are still necessary and update the wiki page and the automated feature detection if possible.
var outName = getTempFile("~preprocess", ".css");
  builder.preprocessCSS(mode, source, outName);
  var out = fs.readFileSync(outName).toString();
  fs.unlinkSync(outName);
  if (cleanup) {
    
    var reg = /\n\/\* Copyright(.|\n)*?Mozilla Foundation(.|\n)*?\*\//g;
    out = out.replace(reg, "");
  }
  var i = source.lastIndexOf("/");
  return createStringSource(source.substr(i + 1), out);
}
function preprocessHTML(source, defines) {