this fixes #940

platform/firefox/frameModule.js

@@ -63,6 +63,23 @@ const getMessageManager = function(win) {
 
 /******************************************************************************/
 
+const getChildProcessMessageManager = function() {
+    var svc = Services;
+    if ( !svc ) {
+        return;
+    }
+    var cpmm = svc.cpmm;
+    if ( cpmm ) {
+        return cpmm;
+    }
+    cpmm = Components.classes['@mozilla.org/childprocessmessagemanager;1'];
+    if ( cpmm ) {
+        return cpmm.getService(Ci.nsISyncMessageSender);
+    }
+};
+
+/******************************************************************************/
+
 var contentObserver = {
     classDescription: 'content-policy for ' + hostName,
     classID: Components.ID('{7afbd130-cbaf-46c2-b944-f5d24305f484}'),
@@ -242,11 +259,9 @@ var contentObserver = {
                 wantXHRConstructor: false
             });
 
-            if ( Services.cpmm ) {
+            if ( getChildProcessMessageManager() ) {
                 sandbox.rpc = function(details) {
-                    var svc = Services;
-                    if ( svc === undefined ) { return; }
-                    var cpmm = svc.cpmm;
+                    var cpmm = getChildProcessMessageManager();
                     if ( !cpmm ) { return; }
                     var r = cpmm.sendSyncMessage(rpcEmitterName, details);
                     if ( Array.isArray(r) ) {

platform/firefox/vapi-background.js

@@ -1712,16 +1712,24 @@ vAPI.rpcReceiver = (function() {
         }
     };
 
-    if ( Services.ppmm ) {
-        Services.ppmm.addMessageListener(
+    var ppmm = Services.ppmm;
+    if ( !ppmm ) {
+        ppmm = Cc['@mozilla.org/parentprocessmessagemanager;1'];
+        if ( ppmm ) {
+            ppmm = ppmm.getService(Ci.nsIMessageListenerManager);
+        }
+    }
+
+    if ( ppmm ) {
+        ppmm.addMessageListener(
             childProcessMessageName,
             onChildProcessMessage
         );
     }
 
     cleanupTasks.push(function() {
-        if ( Services.ppmm ) {
-            Services.ppmm.removeMessageListener(
+        if ( ppmm ) {
+            ppmm.removeMessageListener(
                 childProcessMessageName,
                 onChildProcessMessage
             );