fix https://github.com/gorhill/uBlock/issues/2502#issuecomment-290943606

platform/firefox/bootstrap.js

@@ -101,12 +101,12 @@ function getWindowlessBrowserFrame(appShell) {
     let XPCOMUtils = Components.utils.import('resource://gre/modules/XPCOMUtils.jsm', null).XPCOMUtils;
     windowlessBrowserPL = {
         QueryInterface: XPCOMUtils.generateQI([
-            Ci.nsIWebProgressListener, Ci.nsIWebProgressListener2,
+            Ci.nsIWebProgressListener,
-            Ci.nsISupportsWeakReference]),
+            Ci.nsIWebProgressListener2,
-        onStateChange(wbp, request, stateFlags, status) {
+            Ci.nsISupportsWeakReference
-            if ( !request ) {
+        ]),
-                return;
+        onStateChange: function(wbp, request, stateFlags, status) {
-            }
+            if ( !request ) { return; }
             if ( stateFlags & Ci.nsIWebProgressListener.STATE_STOP ) {
                 webProgress.removeProgressListener(windowlessBrowserPL);
                 windowlessBrowserPL = null;