Fix redirect blocking (http-on-modify-request notification fires delayed starting with Firefox 18)

lib/contentPolicy.js

Index: lib/contentPolicy.js
===================================================================
--- a/lib/contentPolicy.js
+++ b/lib/contentPolicy.js
@@ -366,26 +366,32 @@ let PolicyImplementation =
   {
     let registrar = Components.manager.QueryInterface(Ci.nsIComponentRegistrar);
     registrar.registerFactory(this.classID, this.classDescription, this.contractID, this);
 
     let catMan = Utils.categoryManager;
     for each (let category in this.xpcom_categories)
       catMan.addCategoryEntry(category, this.contractID, this.contractID, false, true);
 
-    Services.obs.addObserver(this, "http-on-modify-request", true);
+    // http-on-opening-request is new in Gecko 18, http-on-modify-request can
+    // be used in earlier releases.
+    let httpTopic = "http-on-opening-request";
+    if (Services.vc.compare(Utils.platformVersion, "18.0") < 0)
+      httpTopic = "http-on-modify-request";
+
+    Services.obs.addObserver(this, httpTopic, true);
     Services.obs.addObserver(this, "content-document-global-created", true);
     Services.obs.addObserver(this, "xpcom-category-entry-removed", true);
     Services.obs.addObserver(this, "xpcom-category-cleared", true);
 
     onShutdown.add(function()
     {
       // Our category observers should be removed before changing category
       // memberships, just in case.
-      Services.obs.removeObserver(this, "http-on-modify-request");
+      Services.obs.removeObserver(this, httpTopic);
       Services.obs.removeObserver(this, "content-document-global-created");
       Services.obs.removeObserver(this, "xpcom-category-entry-removed");
       Services.obs.removeObserver(this, "xpcom-category-cleared");
 
       for each (let category in this.xpcom_categories)
         catMan.deleteCategoryEntry(category, this.contractID, false);
 
       // This needs to run asynchronously, see bug 753687
@@ -431,17 +437,17 @@ let PolicyImplementation =
     // Interpret unknown types as "other"
     if (!(contentType in Policy.typeDescr))
       contentType = Policy.type.OTHER;
 
     let result = Policy.processNode(wnd, node, contentType, location, false);
     if (result)
     {
       // We didn't block this request so we will probably see it again in
-      // http-on-modify-request. Keep it so that we can associate it with the
+      // http-on-opening-request. Keep it so that we can associate it with the
       // channel there - will be needed in case of redirect.
       this.previousRequest = [location, contentType];
     }
     return (result ? Ci.nsIContentPolicy.ACCEPT : Ci.nsIContentPolicy.REJECT_REQUEST);
   },
 
   shouldProcess: function(contentType, contentLocation, requestOrigin, insecNode, mimeType, extra)
   {
@@ -464,26 +470,27 @@ let PolicyImplementation =
         if (!Policy.processNode(subject.opener, subject.opener.document, Policy.type.POPUP, uri, false))
         {
           subject.stop();
           Utils.runAsync(subject.close, subject);
         }
         else if (uri.spec == "about:blank")
         {
           // An about:blank pop-up most likely means that a load will be
-          // initiated synchronously. Set a flag for our "http-on-modify-request"
+          // initiated synchronously. Set a flag for our "http-on-opening-request"
           // handler.
           this.expectingPopupLoad = true;
           Utils.runAsync(function()
           {
             this.expectingPopupLoad = false;
           });
         }
         break;
       }
+      case "http-on-opening-request":
       case "http-on-modify-request":
       {
         if (!(subject instanceof Ci.nsIHttpChannel))
           return;
 
         if (this.previousRequest && subject.URI == this.previousRequest[0] &&
             subject instanceof Ci.nsIWritablePropertyBag)
         {