local patch to retina.js to make it play nicer in firefox

Author: jricher

openid-connect-server-webapp/src/main/webapp/resources/js/lib/retina.js

@@ -80,7 +80,7 @@
  return callback(true);
  } else {
  http = new XMLHttpRequest;
- http.open('HEAD', this.at_2x_path);
+ http.open('GET', this.at_2x_path);
  http.onreadystatechange = function() {
  if (http.readyState != 4) {
  return callback(false);