diff --git a/extensions/firefox/content/PdfStreamConverter.jsm b/extensions/firefox/content/PdfStreamConverter.jsm
index 691d22efd..f4a45a26f 100644
--- a/extensions/firefox/content/PdfStreamConverter.jsm
+++ b/extensions/firefox/content/PdfStreamConverter.jsm
@@ -160,6 +160,25 @@ function getLocalizedString(strings, id, property) {
   return id;
 }
 
+function makeContentReadable(obj, window) {
+//#if MOZCENTRAL
+  return Cu.cloneInto(obj, window);
+//#else
+  if (Cu.cloneInto) {
+    return Cu.cloneInto(obj, window);
+  }
+  if (typeof obj !== 'object' || obj === null) {
+    return obj;
+  }
+  var expose = {};
+  for (let k in obj) {
+    expose[k] = "r";
+  }
+  obj.__exposedProps__ = expose;
+  return obj;
+//#endif
+}
+
 // PDF data storage
 function PdfDataListener(length) {
   this.length = length; // less than 0, if length is unknown
@@ -686,7 +705,7 @@ var StandardChromeActions = (function StandardChromeActionsClosure() {
   return StandardChromeActions;
 })();
 
-// Event listener to trigger chrome privedged code.
+// Event listener to trigger chrome privileged code.
 function RequestListener(actions) {
   this.actions = actions;
 }
@@ -704,21 +723,18 @@ RequestListener.prototype.receive = function(event) {
   }
   if (sync) {
     var response = actions[action].call(this.actions, data);
-    var detail = event.detail;
-    detail.__exposedProps__ = {response: 'r'};
-    detail.response = response;
+    event.detail.response = response;
   } else {
     var response;
-    if (!event.detail.callback) {
+    if (!event.detail.responseExpected) {
       doc.documentElement.removeChild(message);
       response = null;
     } else {
       response = function sendResponse(response) {
         try {
           var listener = doc.createEvent('CustomEvent');
-          listener.initCustomEvent('pdf.js.response', true, false,
-                                   {response: response,
-                                    __exposedProps__: {response: 'r'}});
+          let detail = makeContentReadable({response: response}, doc.defaultView);
+          listener.initCustomEvent('pdf.js.response', true, false, detail);
           return message.dispatchEvent(listener);
         } catch (e) {
           // doc is no longer accessible because the requestor is already
@@ -761,13 +777,13 @@ FindEventManager.prototype.handleEvent = function(e) {
   var contentWindow = this.contentWindow;
   // Only forward the events if they are for our dom window.
   if (chromeWindow.gBrowser.selectedBrowser.contentWindow === contentWindow) {
-    var detail = e.detail;
-    detail.__exposedProps__ = {
-      query: 'r',
-      caseSensitive: 'r',
-      highlightAll: 'r',
-      findPrevious: 'r'
+    var detail = {
+      query: e.detail.query,
+      caseSensitive: e.detail.caseSensitive,
+      highlightAll: e.detail.highlightAll,
+      findPrevious: e.detail.findPrevious
     };
+    detail = makeContentReadable(detail, contentWindow);
     var forward = contentWindow.document.createEvent('CustomEvent');
     forward.initCustomEvent(e.type, true, true, detail);
     contentWindow.dispatchEvent(forward);
diff --git a/web/firefoxcom.js b/web/firefoxcom.js
index 4a5489354..8a775ac75 100644
--- a/web/firefoxcom.js
+++ b/web/firefoxcom.js
@@ -64,9 +64,12 @@ var FirefoxCom = (function FirefoxComClosure() {
       document.documentElement.appendChild(request);
 
       var sender = document.createEvent('CustomEvent');
-      sender.initCustomEvent('pdf.js.message', true, false,
-                             {action: action, data: data, sync: false,
-                              callback: callback});
+      sender.initCustomEvent('pdf.js.message', true, false, {
+        action: action,
+        data: data,
+        sync: false,
+        responseExpected: !!callback
+      });
       return request.dispatchEvent(sender);
     }
   };