only load polyfill in Chrome

u2f-api.js

@@ -10,10 +10,11 @@
 
 'use strict';
 
+if (!('u2f' in window) && 'chrome' in window && chrome.runtime) {
   /** Namespace for the U2F api.
    * @type {Object}
    */
-var u2f = u2f || {};
+  var u2f = {};
 
   /**
    * The U2F extension id
@@ -296,3 +297,4 @@ u2f.register = function(registerRequests, signRequests,
       port.postMessage(req);
     });
   };
+}