--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -4569,34 +4569,29 @@ nsDOMConstructor::HasInstance(nsIXPConne
   *bp = false;
   if (JSVAL_IS_PRIMITIVE(v)) {
     return NS_OK;
   }
 
   JSObject *dom_obj = JSVAL_TO_OBJECT(v);
   NS_ASSERTION(dom_obj, "nsDOMConstructor::HasInstance couldn't get object");
 
-  // This might not be the right object, if XPCNativeWrapping
-  // happened.  Get the wrapped native for this object, then get its
-  // JS object.
-  JSObject *wrapped_obj;
-  nsresult rv = nsContentUtils::XPConnect()->GetJSObjectOfWrapper(cx, dom_obj,
-                                                                  &wrapped_obj);
-  if (NS_SUCCEEDED(rv)) {
-    dom_obj = wrapped_obj;
-  }
+  // This might not be the right object, if there are wrappers. Unwrap if we can.
+  JSObject *wrapped_obj = js::UnwrapObjectChecked(dom_obj, /* stopAtOuter = */ false);
+  if (wrapped_obj)
+      dom_obj = wrapped_obj;
 
   JSClass *dom_class = JS_GetClass(dom_obj);
   if (!dom_class) {
     NS_ERROR("nsDOMConstructor::HasInstance can't get class.");
     return NS_ERROR_UNEXPECTED;
   }
 
   const nsGlobalNameStruct *name_struct;
-  rv = GetNameStruct(NS_ConvertASCIItoUTF16(dom_class->name), &name_struct);
+  nsresult rv = GetNameStruct(NS_ConvertASCIItoUTF16(dom_class->name), &name_struct);
   if (NS_FAILED(rv)) {
     return rv;
   }
 
   if (!name_struct) {
     // This isn't a normal DOM object, see if this constructor lives on its
     // prototype chain.
     jsval val;

--- a/js/xpconnect/idl/nsIXPConnect.idl
+++ b/js/xpconnect/idl/nsIXPConnect.idl
@@ -284,17 +284,17 @@ interface nsIXPCFunctionThisTranslator :
 %{ C++
 // For use with the service manager
 // {CB6593E0-F9B2-11d2-BDD6-000064657374}
 #define NS_XPCONNECT_CID \
 { 0xcb6593e0, 0xf9b2, 0x11d2, \
     { 0xbd, 0xd6, 0x0, 0x0, 0x64, 0x65, 0x73, 0x74 } }
 %}
 
-[uuid(3e825850-3a5f-11e2-81c1-0800200c9a66)]
+[uuid(19e869b4-23cc-417d-b877-f3d46b8bc2d2)]
 interface nsIXPConnect : nsISupports
 {
 %{ C++
   NS_DEFINE_STATIC_CID_ACCESSOR(NS_XPCONNECT_CID)
 %}
 
     /**
      * Initializes classes on a global object that has already been created.
@@ -432,20 +432,16 @@ interface nsIXPConnect : nsISupports
     nsIXPConnectWrappedNative
     getWrappedNativeOfJSObject(in JSContextPtr aJSContext,
                                in JSObjectPtr  aJSObj);
 
     [noscript, notxpcom] nsISupports
     getNativeOfWrapper(in JSContextPtr aJSContext,
                        in JSObjectPtr  aJSObj);
 
-    JSObjectPtr
-    getJSObjectOfWrapper(in JSContextPtr aJSContext,
-                         in JSObjectPtr  aJSObj);
-
     void setSecurityManagerForJSContext(in JSContextPtr aJSContext,
                                         in nsIXPCSecurityManager aManager,
                                         in uint16_t flags);
 
     void getSecurityManagerForJSContext(in JSContextPtr aJSContext,
                                         out nsIXPCSecurityManager aManager,
                                         out uint16_t flags);
 

--- a/js/xpconnect/src/nsXPConnect.cpp
+++ b/js/xpconnect/src/nsXPConnect.cpp
@@ -1367,51 +1367,16 @@ nsXPConnect::GetNativeOfWrapper(JSContex
         XPCWrapper::Unwrap(aJSContext, aJSObj, /* stopAtOuter = */ false);
     JSObject* cur = unsafeObj ? unsafeObj : aJSObj;
     nsISupports* supports = nullptr;
     mozilla::dom::UnwrapDOMObjectToISupports(cur, supports);
     nsCOMPtr<nsISupports> canonical = do_QueryInterface(supports);
     return canonical;
 }
 
-/* JSObjectPtr getJSObjectOfWrapper (in JSContextPtr aJSContext, in JSObjectPtr aJSObj); */
-NS_IMETHODIMP
-nsXPConnect::GetJSObjectOfWrapper(JSContext * aJSContext,
-                                  JSObject * aJSObj,
-                                  JSObject **_retval)
-{
-    NS_ASSERTION(aJSContext, "bad param");
-    NS_ASSERTION(aJSObj, "bad param");
-    NS_ASSERTION(_retval, "bad param");
-
-    XPCCallContext ccx(NATIVE_CALLER, aJSContext);
-    if (!ccx.IsValid())
-        return UnexpectedFailure(NS_ERROR_FAILURE);
-
-    JSObject* obj2 = nullptr;
-    nsIXPConnectWrappedNative* wrapper =
-        XPCWrappedNative::GetWrappedNativeOfJSObject(aJSContext, aJSObj, nullptr,
-                                                     &obj2);
-    if (wrapper) {
-        wrapper->GetJSObject(_retval);
-        return NS_OK;
-    }
-    if (obj2) {
-        *_retval = obj2;
-        return NS_OK;
-    }
-    if (mozilla::dom::IsDOMObject(aJSObj)) {
-        *_retval = aJSObj;
-        return NS_OK;
-    }
-    // else...
-    *_retval = nullptr;
-    return NS_ERROR_FAILURE;
-}
-
 /* nsIXPConnectWrappedNative getWrappedNativeOfNativeObject (in JSContextPtr aJSContext, in JSObjectPtr aScope, in nsISupports aCOMObj, in nsIIDRef aIID); */
 NS_IMETHODIMP
 nsXPConnect::GetWrappedNativeOfNativeObject(JSContext * aJSContext,
                                             JSObject * aScope,
                                             nsISupports *aCOMObj,
                                             const nsIID & aIID,
                                             nsIXPConnectWrappedNative **_retval)
 {