--- a/dom/bindings/BindingUtils.cpp
+++ b/dom/bindings/BindingUtils.cpp
@@ -26,18 +26,16 @@
 #include "nsPrintfCString.h"
 
 #include "mozilla/dom/HTMLObjectElement.h"
 #include "mozilla/dom/HTMLObjectElementBinding.h"
 #include "mozilla/dom/HTMLSharedObjectElement.h"
 #include "mozilla/dom/HTMLEmbedElementBinding.h"
 #include "mozilla/dom/HTMLAppletElementBinding.h"
 
-#include "JavaScriptParent.h"
-
 namespace mozilla {
 namespace dom {
 
 JSErrorFormatString ErrorFormatString[] = {
 #define MSG_DEF(_name, _argc, _str) \
   { _str, _argc, JSEXN_TYPEERR },
 #include "mozilla/dom/Errors.msg"
 #undef MSG_DEF
@@ -1743,27 +1741,16 @@ InterfaceHasInstance(JSContext* cx, JS::
              "ID?");
 
   if (domClass &&
       domClass->mInterfaceChain[clasp->mDepth] == clasp->mPrototypeID) {
     *bp = true;
     return true;
   }
 
-  JS::Rooted<JSObject*> unwrapped(cx, js::CheckedUnwrap(instance, true));
-  if (unwrapped && jsipc::JavaScriptParent::IsCPOW(unwrapped)) {
-    bool boolp = false;
-    if (!jsipc::JavaScriptParent::DOMInstanceOf(unwrapped, clasp->mPrototypeID,
-                                                clasp->mDepth, &boolp)) {
-      return false;
-    }
-    *bp = boolp;
-    return true;
-  }
-
   JS::Rooted<JS::Value> protov(cx);
   DebugOnly<bool> ok = JS_GetProperty(cx, obj, "prototype", &protov);
   MOZ_ASSERT(ok, "Someone messed with our prototype property?");
 
   JS::Rooted<JSObject*> interfacePrototype(cx, &protov.toObject());
   MOZ_ASSERT(IsDOMIfaceAndProtoClass(js::GetObjectClass(interfacePrototype)),
              "Someone messed with our prototype property?");
 
@@ -1795,31 +1782,16 @@ InterfaceHasInstance(JSContext* cx, JS::
     *bp = false;
     return true;
   }
 
   JS::Rooted<JSObject*> instanceObject(cx, &vp.toObject());
   return InterfaceHasInstance(cx, obj, instanceObject, bp);
 }
 
-JSBool
-InterfaceHasInstance(JSContext* cx, int prototypeID, int depth,
-                     JS::Handle<JSObject*> instance,
-                     JSBool* bp)
-{
-  const DOMClass* domClass = GetDOMClass(js::UncheckedUnwrap(instance));
-
-  MOZ_ASSERT(!domClass || prototypeID != prototypes::id::_ID_Count,
-             "Why do we have a hasInstance hook if we don't have a prototype "
-             "ID?");
-
-  *bp = (domClass && domClass->mInterfaceChain[depth] == prototypeID);
-  return true;
-}
-
 bool
 ReportLenientThisUnwrappingFailure(JSContext* cx, JS::Handle<JSObject*> obj)
 {
   GlobalObject global(cx, obj);
   if (global.Failed()) {
     return false;
   }
   nsCOMPtr<nsPIDOMWindow> window = do_QueryInterface(global.Get());

--- a/dom/bindings/BindingUtils.h
+++ b/dom/bindings/BindingUtils.h
@@ -2069,20 +2069,16 @@ ReparentWrapper(JSContext* aCx, JS::Hand
  */
 JSBool
 InterfaceHasInstance(JSContext* cx, JS::Handle<JSObject*> obj,
                      JS::Handle<JSObject*> instance,
                      JSBool* bp);
 JSBool
 InterfaceHasInstance(JSContext* cx, JS::Handle<JSObject*> obj, JS::MutableHandle<JS::Value> vp,
                      JSBool* bp);
-JSBool
-InterfaceHasInstance(JSContext* cx, int prototypeID, int depth,
-                     JS::Handle<JSObject*> instance,
-                     JSBool* bp);
 
 // Helper for lenient getters/setters to report to console.  If this
 // returns false, we couldn't even get a global.
 bool
 ReportLenientThisUnwrappingFailure(JSContext* cx, JS::Handle<JSObject*> obj);
 
 inline JSObject*
 GetUnforgeableHolder(JSObject* aGlobal, prototypes::ID aId)

--- a/dom/bindings/Makefile.in
+++ b/dom/bindings/Makefile.in
@@ -69,17 +69,16 @@ CPPSRCS = \
   CallbackInterface.cpp \
   CallbackObject.cpp \
   DOMJSProxyHandler.cpp \
   $(NULL)
 endif
 
 LOCAL_INCLUDES += -I$(topsrcdir)/js/xpconnect/src \
   -I$(topsrcdir)/js/xpconnect/wrappers \
-  -I$(topsrcdir)/js/ipc \
   -I$(topsrcdir)/content/canvas/src \
   -I$(topsrcdir)/content/html/content/src \
   -I$(topsrcdir)/media/webrtc/signaling/src/peerconnection \
   -I$(topsrcdir)/dom/base \
   -I$(topsrcdir)/dom/battery \
   -I$(topsrcdir)/dom/indexedDB \
   -I$(topsrcdir)/content/xslt/src/base \
   -I$(topsrcdir)/content/xslt/src/xpath \

--- a/js/ipc/JavaScriptChild.cpp
+++ b/js/ipc/JavaScriptChild.cpp
@@ -2,17 +2,16 @@
  * vim: set ts=4 sw=4 et tw=80:
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "JavaScriptChild.h"
 #include "mozilla/dom/ContentChild.h"
-#include "mozilla/dom/BindingUtils.h"
 #include "nsContentUtils.h"
 #include "xpcprivate.h"
 #include "jsfriendapi.h"
 #include "nsCxPusher.h"
 
 using namespace JS;
 using namespace mozilla;
 using namespace mozilla::jsipc;
@@ -621,32 +620,8 @@ JavaScriptChild::AnswerInstanceOf(const 
     ConvertID(iid, &nsiid);
 
     nsresult rv = xpc::HasInstance(cx, obj, &nsiid, instanceof);
     if (rv != NS_OK)
         return fail(cx, rs);
 
     return ok(rs);
 }
-
-bool
-JavaScriptChild::AnswerDOMInstanceOf(const ObjectId &objId, const int &prototypeID,
-                                     const int &depth,
-                                     ReturnStatus *rs, bool *instanceof)
-{
-    AutoSafeJSContext cx;
-    JSAutoRequest request(cx);
-
-    *instanceof = false;
-
-    RootedObject obj(cx, findObject(objId));
-    if (!obj)
-        return false;
-
-    JSAutoCompartment comp(cx, obj);
-
-    JSBool tmp;
-    if (!mozilla::dom::InterfaceHasInstance(cx, prototypeID, depth, obj, &tmp))
-        return fail(cx, rs);
-    *instanceof = tmp;
-
-    return ok(rs);
-}

--- a/js/ipc/JavaScriptChild.h
+++ b/js/ipc/JavaScriptChild.h
@@ -61,18 +61,16 @@ class JavaScriptChild
     bool AnswerObjectClassIs(const ObjectId &objId, const uint32_t &classValue,
                              bool *result);
     bool AnswerClassName(const ObjectId &objId, nsString *result);
 
     bool AnswerGetPropertyNames(const ObjectId &objId, const uint32_t &flags,
                                 ReturnStatus *rs, nsTArray<nsString> *names);
     bool AnswerInstanceOf(const ObjectId &objId, const JSIID &iid,
                           ReturnStatus *rs, bool *instanceof);
-    bool AnswerDOMInstanceOf(const ObjectId &objId, const int &prototypeID, const int &depth,
-                             ReturnStatus *rs, bool *instanceof);
 
   protected:
     JSObject *unwrap(JSContext *cx, ObjectId id);
 
   private:
     bool makeId(JSContext *cx, JSObject *obj, ObjectId *idp);
     bool fail(JSContext *cx, ReturnStatus *rs);
     bool ok(ReturnStatus *rs);

--- a/js/ipc/JavaScriptParent.cpp
+++ b/js/ipc/JavaScriptParent.cpp
@@ -509,18 +509,17 @@ JavaScriptParent::init()
         return false;
 
     return true;
 }
 
 bool
 JavaScriptParent::makeId(JSContext *cx, JSObject *obj, ObjectId *idp)
 {
-    obj = js::CheckedUnwrap(obj, false);
-    if (!obj || !IsProxy(obj) || GetProxyHandler(obj) != &CPOWProxyHandler::singleton) {
+    if (!IsProxy(obj) || GetProxyHandler(obj) != &CPOWProxyHandler::singleton) {
         JS_ReportError(cx, "cannot ipc non-cpow object");
         return false;
     }
 
     *idp = idOf(obj);
     return true;
 }
 
@@ -652,29 +651,8 @@ JavaScriptParent::instanceOf(JSObject *o
     if (!CallInstanceOf(objId, iid, &status, bp))
         return NS_ERROR_UNEXPECTED;
 
     if (!status.ok())
         return NS_ERROR_UNEXPECTED;
 
     return NS_OK;
 }
-
-/* static */ bool
-JavaScriptParent::DOMInstanceOf(JSObject *obj, int prototypeID, int depth, bool *bp)
-{
-    return ParentOf(obj)->domInstanceOf(obj, prototypeID, depth, bp);
-}
-
-bool
-JavaScriptParent::domInstanceOf(JSObject *obj, int prototypeID, int depth, bool *bp)
-{
-    ObjectId objId = idOf(obj);
-
-    ReturnStatus status;
-    if (!CallDOMInstanceOf(objId, prototypeID, depth, &status, bp))
-        return false;
-
-    if (!status.ok())
-        return false;
-
-    return true;
-}

--- a/js/ipc/JavaScriptParent.h
+++ b/js/ipc/JavaScriptParent.h
@@ -61,26 +61,19 @@ class JavaScriptParent
 
     void decref();
     void incref();
     void destroyFromContent();
 
     void drop(JSObject *obj);
 
     static bool IsCPOW(JSObject *obj);
-
     static nsresult InstanceOf(JSObject *obj, const nsID *id, bool *bp);
-    nsresult instanceOf(JSObject *obj, const nsID *id, bool *bp);
 
-    /*
-     * Check that |obj| is a DOM wrapper whose prototype chain contains
-     * |prototypeID| at depth |depth|.
-     */
-    static bool DOMInstanceOf(JSObject *obj, int prototypeID, int depth, bool *bp);
-    bool domInstanceOf(JSObject *obj, int prototypeID, int depth, bool *bp);
+    nsresult instanceOf(JSObject *obj, const nsID *id, bool *bp);
 
   protected:
     JSObject *unwrap(JSContext *cx, ObjectId objId);
 
   private:
     bool makeId(JSContext *cx, JSObject *obj, ObjectId *idp);
     bool getPropertyNames(JSContext *cx, JS::HandleObject proxy, uint32_t flags, js::AutoIdVector &props);
     ObjectId idOf(JSObject *obj);

--- a/js/ipc/PJavaScript.ipdl
+++ b/js/ipc/PJavaScript.ipdl
@@ -36,16 +36,15 @@ child:
 
     urgent IsExtensible(uint64_t objId) returns (ReturnStatus rs, bool result);
     urgent Call(uint64_t objId, JSParam[] argv) returns (ReturnStatus rs, JSVariant result, JSParam[] outparams);
     urgent ObjectClassIs(uint64_t objId, uint32_t classValue) returns (bool result);
     urgent ClassName(uint64_t objId) returns (nsString name);
 
     urgent GetPropertyNames(uint64_t objId, uint32_t flags) returns (ReturnStatus rs, nsString[] names);
     urgent InstanceOf(uint64_t objId, JSIID iid) returns (ReturnStatus rs, bool instanceof);
-    urgent DOMInstanceOf(uint64_t objId, int prototypeID, int depth) returns (ReturnStatus rs, bool instanceof);
 
 parent:
     async __delete__();
 };
 
 }
 }