Update alert message regarding Firefox version (#1870)

Author: silvanshade

examples/raytrace-parallel/index.js

@@ -12,7 +12,7 @@ concurrency.disabled = true;
 
 // First up, but try to do feature detection to provide better error messages
 function loadWasm() {
-  let msg = 'This demo currently requires Firefox Nightly (64.0) with\n'
+  let msg = 'This demo requires a current version of Firefox (e.g., 70.0) with\n'
   msg += 'the `javascript.options.shared_memory` option enabled in `about:config`';
   if (typeof SharedArrayBuffer !== 'function') {
     alert('this browser does not have SharedArrayBuffer support enabled' + '\n\n' + msg);