Firefox: STATE_TRANSFERRING did not fire

Question

I have just modify a snippet from this page: https://developer.mozilla.org/en/Code_snippets/Progress_Listeners

But with this code only STATE_START and STATE_STOP were fired. The rest did not fire at all

        var target = this;
        const STATE_START = Components.interfaces.nsIWebProgressListener.STATE_START;
        const STATE_REDIRECTING = Components.interfaces.nsIWebProgressListener.STATE_REDIRECTING;
        const STATE_TRANSFERRING = Components.interfaces.nsIWebProgressListener.STATE_TRANSFERRING;
        const STATE_NEGOTIATING = Components.interfaces.nsIWebProgressListener.STATE_NEGOTIATING;
        const STATE_STOP = Components.interfaces.nsIWebProgressListener.STATE_STOP;
        var myListener =
        {
          QueryInterface: function(aIID)
          {
           if (aIID.equals(Components.interfaces.nsIWebProgressListener) ||
               aIID.equals(Components.interfaces.nsISupportsWeakReference) ||
               aIID.equals(Components.interfaces.nsISupports))
             return this;
           throw Components.results.NS_NOINTERFACE;
          },

          onStateChange: function(aWebProgress, aRequest, aFlag, aStatus)
          {
           // If you use myListener for more than one tab/window, use
           // aWebProgress.DOMWindow to obtain the tab/window which triggers the state change
           if(aFlag & STATE_START)
           {
                target.log("start")
             // This fires when the load event is initiated
           }
           if(aFlag & STATE_REDIRECTING)
           {
            target.log("redirecting");
           }
           if(aFlag & STATE_TRANSFERRING)
           {
            target.log("transferring");
           }
           if(aFlag & STATE_NEGOTIATING)
           {
            target.log("negotiating");
           }
           if(aFlag & STATE_STOP)
           {
            target.log("stop");
             // This fires when the load finishes
           }
          },

          onLocationChange: function(aProgress, aRequest, aURI)
          {
           // This fires when the location bar changes; i.e load event is confirmed
           // or when the user switches tabs. If you use myListener for more than one tab/window,
           // use aProgress.DOMWindow to obtain the tab/window which triggered the change.
          },

          // For definitions of the remaining functions see related documentation
          onProgressChange: function(aWebProgress, aRequest, curSelf, maxSelf, curTot, maxTot) { },
          onStatusChange: function(aWebProgress, aRequest, aStatus, aMessage) { },
          onSecurityChange: function(aWebProgress, aRequest, aState) { }
        }
        gBrowser.addProgressListener(myListener);