--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -976,19 +976,17 @@ nsDOMConstructor::HasInstance(nsIXPConne
 
   if (name_struct == class_name_struct) {
     *bp = true;
 
     return NS_OK;
   }
 
   const nsIID *class_iid;
-  if (class_name_struct->mType == nsGlobalNameStruct::eTypeClassProto) {
-    class_iid = &class_name_struct->mIID;
-  } else if (class_name_struct->mType == nsGlobalNameStruct::eTypeClassConstructor) {
+  if (class_name_struct->mType == nsGlobalNameStruct::eTypeClassConstructor) {
     class_iid =
       sClassInfoData[class_name_struct->mDOMClassInfoID].mProtoChainInterface;
   } else {
     *bp = false;
 
     return NS_OK;
   }
 
@@ -1039,19 +1037,17 @@ nsDOMConstructor::HasInstance(nsIXPConne
 nsresult
 nsDOMConstructor::ResolveInterfaceConstants(JSContext *cx, JS::Handle<JSObject*> obj)
 {
   const nsGlobalNameStruct *class_name_struct = GetNameStruct();
   if (!class_name_struct)
     return NS_ERROR_UNEXPECTED;
 
   const nsIID *class_iid;
-  if (class_name_struct->mType == nsGlobalNameStruct::eTypeClassProto) {
-    class_iid = &class_name_struct->mIID;
-  } else if (class_name_struct->mType == nsGlobalNameStruct::eTypeClassConstructor) {
+  if (class_name_struct->mType == nsGlobalNameStruct::eTypeClassConstructor) {
     class_iid =
       sClassInfoData[class_name_struct->mDOMClassInfoID].mProtoChainInterface;
   } else {
     return NS_OK;
   }
 
   nsresult rv = DefineInterfaceConstants(cx, obj, class_iid);
   NS_ENSURE_SUCCESS(rv, rv);
@@ -1088,32 +1084,28 @@ GetXPCProto(nsIXPConnect *aXPConnect, JS
 
   nsresult rv =
     aXPConnect->GetWrappedNativePrototype(cx, aWin->GetGlobalJSObject(), ci, aProto.address());
   NS_ENSURE_SUCCESS(rv, rv);
 
   return JS_WrapObject(cx, aProto) ? NS_OK : NS_ERROR_FAILURE;
 }
 
-// Either ci_data must be non-null or name_struct must be non-null and of type
-// eTypeClassProto.
+// ci_data must be non-null
 static nsresult
 ResolvePrototype(nsIXPConnect *aXPConnect, nsGlobalWindowInner *aWin, JSContext *cx,
                  JS::Handle<JSObject*> obj, const char16_t *name,
                  const nsDOMClassInfoData *ci_data,
                  const nsGlobalNameStruct *name_struct,
                  nsScriptNameSpaceManager *nameSpaceManager,
                  JSObject* aDot_prototype,
                  JS::MutableHandle<JS::PropertyDescriptor> ctorDesc)
 {
   JS::Rooted<JSObject*> dot_prototype(cx, aDot_prototype);
-  NS_ASSERTION(ci_data ||
-               (name_struct &&
-                name_struct->mType == nsGlobalNameStruct::eTypeClassProto),
-               "Wrong type or missing ci_data!");
+  NS_ASSERTION(ci_data, "Missing ci_data!");
 
   RefPtr<nsDOMConstructor> constructor;
   nsresult rv = nsDOMConstructor::Create(name, name_struct, aWin->AsInner(),
                                          getter_AddRefs(constructor));
   NS_ENSURE_SUCCESS(rv, rv);
 
   JS::Rooted<JS::Value> v(cx);
 
@@ -1130,20 +1122,17 @@ ResolvePrototype(nsIXPConnect *aXPConnec
   if (!JS_WrapValue(cx, ctorDesc.value())) {
     return NS_ERROR_UNEXPECTED;
   }
 
   JS::Rooted<JSObject*> class_obj(cx, &v.toObject());
 
   const nsIID *primary_iid = &NS_GET_IID(nsISupports);
 
-  if (!ci_data) {
-    primary_iid = &name_struct->mIID;
-  }
-  else if (ci_data->mProtoChainInterface) {
+  if (ci_data->mProtoChainInterface) {
     primary_iid = ci_data->mProtoChainInterface;
   }
 
   nsCOMPtr<nsIInterfaceInfo> if_info;
   nsCOMPtr<nsIInterfaceInfo> parent;
   const char *class_parent_name = nullptr;
 
   if (!primary_iid->Equals(NS_GET_IID(nsISupports))) {
@@ -1156,28 +1145,28 @@ ResolvePrototype(nsIXPConnect *aXPConnec
       iim(do_GetService(NS_INTERFACEINFOMANAGER_SERVICE_CONTRACTID));
     NS_ENSURE_TRUE(iim, NS_ERROR_NOT_AVAILABLE);
 
     iim->GetInfoForIID(primary_iid, getter_AddRefs(if_info));
     NS_ENSURE_TRUE(if_info, NS_ERROR_UNEXPECTED);
 
     const nsIID *iid = nullptr;
 
-    if (ci_data && !ci_data->mHasClassInterface) {
+    if (!ci_data->mHasClassInterface) {
       if_info->GetIIDShared(&iid);
     } else {
       if_info->GetParent(getter_AddRefs(parent));
       NS_ENSURE_TRUE(parent, NS_ERROR_UNEXPECTED);
 
       parent->GetIIDShared(&iid);
     }
 
     if (iid) {
       if (!iid->Equals(NS_GET_IID(nsISupports))) {
-        if (ci_data && !ci_data->mHasClassInterface) {
+        if (!ci_data->mHasClassInterface) {
           // If the class doesn't have a class interface the primary
           // interface is the interface that should be
           // constructor.prototype.__proto__.
 
           if_info->GetNameShared(&class_parent_name);
         } else {
           // If the class does have a class interface (or there's no
           // real class for this name) then the parent of the
@@ -1372,24 +1361,16 @@ nsWindowSH::GlobalResolve(nsGlobalWindow
     // prototype.
     return ResolvePrototype(nsDOMClassInfo::sXPConnect, aWin, cx, obj,
                             class_name,
                             &sClassInfoData[name_struct->mDOMClassInfoID],
                             name_struct, nameSpaceManager, dot_prototype,
                             desc);
   }
 
-  if (name_struct->mType == nsGlobalNameStruct::eTypeClassProto) {
-    // We don't have a XPConnect prototype object, let ResolvePrototype create
-    // one.
-    return ResolvePrototype(nsDOMClassInfo::sXPConnect, aWin, cx, obj,
-                            class_name, nullptr,
-                            name_struct, nameSpaceManager, nullptr, desc);
-  }
-
   if (name_struct->mType == nsGlobalNameStruct::eTypeProperty) {
     // Before defining a global property, check for a named subframe of the
     // same name. If it exists, we don't want to shadow it.
     if (nsCOMPtr<nsPIDOMWindowOuter> childWin = aWin->GetChildWindow(name)) {
       return NS_OK;
     }
 
     nsCOMPtr<nsISupports> native(do_CreateInstance(name_struct->mCID, &rv));

--- a/dom/base/nsScriptNameSpaceManager.h
+++ b/dom/base/nsScriptNameSpaceManager.h
@@ -20,23 +20,21 @@
 #include "xpcpublic.h"
 
 struct nsGlobalNameStruct
 {
   enum nametype {
     eTypeNotInitialized,
     eTypeProperty,
     eTypeClassConstructor,
-    eTypeClassProto,
   } mType;
 
   union {
     int32_t mDOMClassInfoID; // eTypeClassConstructor
-    nsIID mIID; // eTypeClassProto
-    nsCID mCID; // All other types
+    nsCID mCID; // eTypeProperty
   };
 };
 
 class GlobalNameMapEntry : public PLDHashEntryHdr
 {
 public:
   // Our hash table ops don't care about the order of these members.
   nsString mKey;