diff --git a/dom/bindings/BindingUtils.h b/dom/bindings/BindingUtils.h
index 5fcc4935cdf5..708c18a383c1 100644
--- a/dom/bindings/BindingUtils.h
+++ b/dom/bindings/BindingUtils.h
@@ -291,13 +291,17 @@ IsConvertibleToCallbackInterface(JSContext* cx, JS::Handle<JSObject*> obj)
   return IsNotDateOrRegExp(cx, obj);
 }
 
-// The items in the protoAndIfaceCache are indexed by the prototypes::id::ID and
-// constructors::id::ID enums, in that order. The end of the prototype objects
-// should be the start of the interface objects.
+// The items in the protoAndIfaceCache are indexed by the prototypes::id::ID,
+// constructors::id::ID and namedpropertiesobjects::id::ID enums, in that order.
+// The end of the prototype objects should be the start of the interface
+// objects, and the end of the interface objects should be the start of the
+// named properties objects.
 static_assert((size_t)constructors::id::_ID_Start ==
-              (size_t)prototypes::id::_ID_Count,
+              (size_t)prototypes::id::_ID_Count &&
+              (size_t)namedpropertiesobjects::id::_ID_Start ==
+              (size_t)constructors::id::_ID_Count,
               "Overlapping or discontiguous indexes.");
-const size_t kProtoAndIfaceCacheCount = constructors::id::_ID_Count;
+const size_t kProtoAndIfaceCacheCount = namedpropertiesobjects::id::_ID_Count;
 
 class ProtoAndIfaceCache
 {
diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 60e40f31d5df..686a47347e62 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -2581,8 +2581,8 @@ class CGCreateInterfaceObjectsMethod(CGAbstractMethod):
     def definition_body(self):
         parentProtoName = self.descriptor.parentPrototypeName
         if self.descriptor.hasNamedPropertiesObject:
-            parentProtoType = "Rooted"
-            getParentProto = "aCx, GetNamedPropertiesObject(aCx, aGlobal)"
+            parentProtoType = "Handle"
+            getParentProto = "GetNamedPropertiesObject(aCx, aGlobal)"
         elif parentProtoName is None:
             parentProtoType = "Rooted"
             if self.descriptor.interface.getExtendedAttribute("ArrayClass"):
@@ -2856,7 +2856,7 @@ class CGGetNamedPropertiesObjectMethod(CGAbstractStaticMethod):
                 Argument('JS::Handle<JSObject*>', 'aGlobal')]
         CGAbstractStaticMethod.__init__(self, descriptor,
                                         'GetNamedPropertiesObject',
-                                        'JSObject*', args)
+                                        'JS::Handle<JSObject*>', args)
 
     def definition_body(self):
         parentProtoName = self.descriptor.parentPrototypeName
@@ -2868,17 +2868,30 @@ class CGGetNamedPropertiesObjectMethod(CGAbstractStaticMethod):
                 """
                 JS::Rooted<JSObject*> parentProto(aCx, ${parent}::GetProtoObject(aCx, aGlobal));
                 if (!parentProto) {
-                  return nullptr;
+                  return js::NullPtr();
                 }
                 """,
                 parent=toBindingNamespace(parentProtoName))
             parentProto = "parentProto"
         return fill(
             """
-            $*{getParentProto}
-            return ${nativeType}::CreateNamedPropertiesObject(aCx, ${parentProto});
+            /* Make sure our global is sane.  Hopefully we can remove this sometime */
+            if (!(js::GetObjectClass(aGlobal)->flags & JSCLASS_DOM_GLOBAL)) {
+              return JS::NullPtr();
+            }
+
+            /* Check to see whether the named properties object has already been created */
+            ProtoAndIfaceCache& protoAndIfaceCache = *GetProtoAndIfaceCache(aGlobal);
+
+            JS::Heap<JSObject*>& namedPropertiesObject = protoAndIfaceCache.EntrySlotOrCreate(namedpropertiesobjects::id::${ifaceName});
+            if (!namedPropertiesObject) {
+              $*{getParentProto}
+              namedPropertiesObject = ${nativeType}::CreateNamedPropertiesObject(aCx, ${parentProto});
+            }
+            return JS::Handle<JSObject*>::fromMarkedLocation(namedPropertiesObject.address());
             """,
             getParentProto=getParentProto,
+            ifaceName=self.descriptor.name,
             parentProto=parentProto,
             nativeType=self.descriptor.nativeType)
 
@@ -14209,6 +14222,18 @@ class GlobalGenRoots():
 
         curr.append(idEnum)
 
+        # Named properties object enum.
+        namedPropertiesObjects = [d.name for d in config.getDescriptors(hasNamedPropertiesObject=True)]
+        idEnum = CGNamespacedEnum('id', 'ID', ['_ID_Start'] + namedPropertiesObjects,
+                                  ['constructors::id::_ID_Count', '_ID_Start'])
+
+        # Wrap all of that in our namespaces.
+        idEnum = CGNamespace.build(['mozilla', 'dom', 'namedpropertiesobjects'],
+                                   CGWrapper(idEnum, pre='\n'))
+        idEnum = CGWrapper(idEnum, post='\n')
+
+        curr.append(idEnum)
+
         traitsDecls = [CGGeneric(declare=dedent("""
             template <prototypes::ID PrototypeID>
             struct PrototypeTraits;