Updating comments in custom Modernizr tests

Author: rileytb

packages/react-scripts/layout/views/partials/featureDetection.ejs

@@ -1,10 +1,13 @@
 if (Modernizr) {
   const unsupportedBrowserHeader = document.getElementById('unsupported-browser');
 
+  <%# Handles Chrome/Edge v84 and lower %>
   Modernizr.addTest('replaceAll', () => {
       return typeof String.prototype.replaceAll === 'function';
   });
 
+  <%# Handles Firefox v90/Safari v15 and lower %>
+  <%# Written with eval because declaring a function with private class fields threw an error outside of the catch %>
   Modernizr.addTest('privateFields', () => {
     try {
       eval("class Test { #privateField; }");
@@ -14,10 +17,8 @@ if (Modernizr) {
     }
   });
 
-  const outdatedFeatures = Object.keys(Modernizr).filter(feature => !Modernizr[feature]);
-
   if (unsupportedBrowserHeader) {
-    if (outdatedFeatures.length > 0) {
+    if (Object.keys(Modernizr).filter(feature => !Modernizr[feature]).length > 0) {
       unsupportedBrowserHeader.style.display = 'block';
     } else {
       unsupportedBrowserHeader.remove();