diff --git a/content/xbl/src/nsXBLBinding.cpp b/content/xbl/src/nsXBLBinding.cpp
index c2e48f8fd846..e5ff15be2741 100644
--- a/content/xbl/src/nsXBLBinding.cpp
+++ b/content/xbl/src/nsXBLBinding.cpp
@@ -101,7 +101,8 @@ nsXBLJSClass::nsXBLJSClass(const nsAFlatCString& aClassName,
     JSCLASS_NEW_RESOLVE |
     // Our one reserved slot holds the relevant nsXBLPrototypeBinding
     JSCLASS_HAS_RESERVED_SLOTS(1);
-  addProperty = delProperty = getProperty = ::JS_PropertyStub;
+  addProperty = getProperty = ::JS_PropertyStub;
+  delProperty = ::JS_DeletePropertyStub;
   setProperty = ::JS_StrictPropertyStub;
   enumerate = XBLEnumerate;
   resolve = JS_ResolveStub;
diff --git a/content/xbl/src/nsXBLDocumentInfo.cpp b/content/xbl/src/nsXBLDocumentInfo.cpp
index 16cca7e11e47..fef1da79af36 100644
--- a/content/xbl/src/nsXBLDocumentInfo.cpp
+++ b/content/xbl/src/nsXBLDocumentInfo.cpp
@@ -173,7 +173,7 @@ JSClass nsXBLDocGlobalObject::gSharedGlobalClass = {
     "nsXBLPrototypeScript compilation scope",
     JSCLASS_HAS_PRIVATE | JSCLASS_PRIVATE_IS_NSISUPPORTS |
     JSCLASS_IMPLEMENTS_BARRIERS | JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(0),
-    JS_PropertyStub,  JS_PropertyStub,
+    JS_PropertyStub,  JS_DeletePropertyStub,
     nsXBLDocGlobalObject_getProperty, nsXBLDocGlobalObject_setProperty,
     JS_EnumerateStub, nsXBLDocGlobalObject_resolve,
     JS_ConvertStub, nsXBLDocGlobalObject_finalize,
diff --git a/content/xul/document/src/nsXULPrototypeDocument.cpp b/content/xul/document/src/nsXULPrototypeDocument.cpp
index 8a1bd0500311..a3b04196caac 100644
--- a/content/xul/document/src/nsXULPrototypeDocument.cpp
+++ b/content/xul/document/src/nsXULPrototypeDocument.cpp
@@ -114,7 +114,7 @@ JSClass nsXULPDGlobalObject::gSharedGlobalClass = {
     "nsXULPrototypeScript compilation scope",
     JSCLASS_HAS_PRIVATE | JSCLASS_PRIVATE_IS_NSISUPPORTS |
     JSCLASS_IMPLEMENTS_BARRIERS | JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(0),
-    JS_PropertyStub,  JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub,  JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, nsXULPDGlobalObject_resolve,  JS_ConvertStub,
     nsXULPDGlobalObject_finalize, nullptr, nullptr, nullptr, nullptr,
     nullptr
diff --git a/dom/base/nsDOMClassInfo.cpp b/dom/base/nsDOMClassInfo.cpp
index ebe23a56adc0..3a7a3c3cf3fb 100644
--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -1386,7 +1386,7 @@ NS_INTERFACE_MAP_END
 
 static JSClass sDOMConstructorProtoClass = {
   "DOM Constructor.prototype", 0,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, nullptr
 };
 
@@ -2681,8 +2681,7 @@ nsDOMClassInfo::AddProperty(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
 
 NS_IMETHODIMP
 nsDOMClassInfo::DelProperty(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
-                            JSObject *obj, jsid id, jsval *vp,
-                            bool *_retval)
+                            JSObject *obj, jsid id, bool *_retval)
 {
   NS_WARNING("nsDOMClassInfo::DelProperty Don't call me!");
 
@@ -3176,7 +3175,7 @@ static JSClass sGlobalScopePolluterClass = {
   "Global Scope Polluter",
   JSCLASS_NEW_RESOLVE,
   JS_PropertyStub,
-  JS_PropertyStub,
+  JS_DeletePropertyStub,
   nsWindowSH::GlobalScopePolluterGetProperty,
   JS_StrictPropertyStub,
   JS_EnumerateStub,
@@ -6316,7 +6315,7 @@ static JSClass sHTMLDocumentAllClass = {
   JSCLASS_HAS_PRIVATE | JSCLASS_PRIVATE_IS_NSISUPPORTS | JSCLASS_NEW_RESOLVE |
   JSCLASS_EMULATES_UNDEFINED | JSCLASS_HAS_RESERVED_SLOTS(1),
   JS_PropertyStub,                                         /* addProperty */
-  JS_PropertyStub,                                         /* delProperty */
+  JS_DeletePropertyStub,                                   /* delProperty */
   nsHTMLDocumentSH::DocumentAllGetProperty,                /* getProperty */
   JS_StrictPropertyStub,                                   /* setProperty */
   JS_EnumerateStub,
@@ -6332,7 +6331,7 @@ static JSClass sHTMLDocumentAllHelperClass = {
   "HTML document.all helper class",
   JSCLASS_NEW_RESOLVE,
   JS_PropertyStub,                                         /* addProperty */
-  JS_PropertyStub,                                         /* delProperty */
+  JS_DeletePropertyStub,                                   /* delProperty */
   nsHTMLDocumentSH::DocumentAllHelperGetProperty,          /* getProperty */
   JS_StrictPropertyStub,                                   /* setProperty */
   JS_EnumerateStub,
@@ -6345,7 +6344,7 @@ static JSClass sHTMLDocumentAllTagsClass = {
   "HTML document.all.tags class",
   JSCLASS_HAS_PRIVATE | JSCLASS_NEW_RESOLVE | JSCLASS_PRIVATE_IS_NSISUPPORTS,
   JS_PropertyStub,                                         /* addProperty */
-  JS_PropertyStub,                                         /* delProperty */
+  JS_DeletePropertyStub,                                   /* delProperty */
   JS_PropertyStub,                                         /* getProperty */
   JS_StrictPropertyStub,                                   /* setProperty */
   JS_EnumerateStub,
@@ -7429,7 +7428,7 @@ nsStorage2SH::SetProperty(nsIXPConnectWrappedNative *wrapper,
 NS_IMETHODIMP
 nsStorage2SH::DelProperty(nsIXPConnectWrappedNative *wrapper,
                           JSContext *cx, JSObject *obj, jsid id,
-                          jsval *vp, bool *_retval)
+                          bool *_retval)
 {
   nsCOMPtr<nsIDOMStorage> storage(do_QueryWrappedNative(wrapper));
   NS_ENSURE_TRUE(storage, NS_ERROR_UNEXPECTED);
@@ -7441,11 +7440,12 @@ nsStorage2SH::DelProperty(nsIXPConnectWrappedNative *wrapper,
   NS_ENSURE_TRUE(keyStr.init(cx, key), NS_ERROR_UNEXPECTED);
 
   nsresult rv = storage->RemoveItem(keyStr);
-  if (NS_SUCCEEDED(rv)) {
-    rv = NS_SUCCESS_I_DID_SOMETHING;
+  if (NS_FAILED(rv)) {
+    return rv;
   }
 
-  return rv;
+  *_retval = true;
+  return NS_SUCCESS_I_DID_SOMETHING;
 }
 
 
diff --git a/dom/base/nsDOMClassInfo.h b/dom/base/nsDOMClassInfo.h
index bb16a11f48fd..a4cdc6adb246 100644
--- a/dom/base/nsDOMClassInfo.h
+++ b/dom/base/nsDOMClassInfo.h
@@ -1041,7 +1041,7 @@ protected:
   NS_IMETHOD GetProperty(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
                          JSObject *obj, jsid id, jsval *vp, bool *_retval);
   NS_IMETHOD DelProperty(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
-                         JSObject *obj, jsid id, jsval *vp, bool *_retval);
+                         JSObject *obj, jsid id, bool *_retval);
   NS_IMETHOD NewEnumerate(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
                           JSObject *obj, uint32_t enum_op, jsval *statep,
                           jsid *idp, bool *_retval);
diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 8e3e027c1355..aca253ae9aea 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -174,7 +174,7 @@ DOMJSClass Class = {
   { "%s",
     %s,
     %s, /* addProperty */
-    JS_PropertyStub,       /* delProperty */
+    JS_DeletePropertyStub, /* delProperty */
     JS_PropertyStub,       /* getProperty */
     JS_StrictPropertyStub, /* setProperty */
     JS_EnumerateStub,
@@ -223,7 +223,7 @@ class CGPrototypeJSClass(CGThing):
     "%sPrototype",
     JSCLASS_IS_DOMIFACEANDPROTOJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(2),
     JS_PropertyStub,       /* addProperty */
-    JS_PropertyStub,       /* delProperty */
+    JS_DeletePropertyStub, /* delProperty */
     JS_PropertyStub,       /* getProperty */
     JS_StrictPropertyStub, /* setProperty */
     JS_EnumerateStub,
@@ -277,7 +277,7 @@ static DOMIfaceAndProtoJSClass InterfaceObjectClass = {
     "Function",
     JSCLASS_IS_DOMIFACEANDPROTOJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(DOM_INTERFACE_SLOTS_BASE + %i),
     JS_PropertyStub,       /* addProperty */
-    JS_PropertyStub,       /* delProperty */
+    JS_DeletePropertyStub, /* delProperty */
     JS_PropertyStub,       /* getProperty */
     JS_StrictPropertyStub, /* setProperty */
     JS_EnumerateStub,
diff --git a/dom/indexedDB/IDBObjectStore.cpp b/dom/indexedDB/IDBObjectStore.cpp
index 9519ba58b90d..2ab1060cd5d0 100644
--- a/dom/indexedDB/IDBObjectStore.cpp
+++ b/dom/indexedDB/IDBObjectStore.cpp
@@ -570,7 +570,7 @@ class ThreadLocalJSRuntime
 JSClass ThreadLocalJSRuntime::sGlobalClass = {
   "IndexedDBTransactionThreadGlobal",
   JSCLASS_GLOBAL_FLAGS,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
@@ -835,7 +835,7 @@ public:
 
 JSClass IDBObjectStore::sDummyPropJSClass = {
   "dummy", 0,
-  JS_PropertyStub,  JS_PropertyStub,
+  JS_PropertyStub,  JS_DeletePropertyStub,
   JS_PropertyStub,  JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub,
   JS_ConvertStub
diff --git a/dom/plugins/base/nsJSNPRuntime.cpp b/dom/plugins/base/nsJSNPRuntime.cpp
index f629afad7ca7..4f600ffe32e6 100644
--- a/dom/plugins/base/nsJSNPRuntime.cpp
+++ b/dom/plugins/base/nsJSNPRuntime.cpp
@@ -115,7 +115,7 @@ static JSBool
 NPObjWrapper_AddProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMutableHandleValue vp);
 
 static JSBool
-NPObjWrapper_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMutableHandleValue vp);
+NPObjWrapper_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSBool *succeeded);
 
 static JSBool
 NPObjWrapper_SetProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSBool strict,
@@ -188,7 +188,7 @@ NPObjectMember_Trace(JSTracer *trc, JSObject *obj);
 static JSClass sNPObjectMemberClass =
   {
     "NPObject Ambiguous Member class", JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS,
-    JS_PropertyStub, JS_PropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub,
     JS_PropertyStub, JS_StrictPropertyStub, JS_EnumerateStub,
     JS_ResolveStub, NPObjectMember_Convert,
     NPObjectMember_Finalize, nullptr, NPObjectMember_Call,
@@ -1197,7 +1197,7 @@ NPObjWrapper_AddProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMut
 }
 
 static JSBool
-NPObjWrapper_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMutableHandleValue vp)
+NPObjWrapper_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSBool *succeeded)
 {
   NPObject *npobj = GetNPObject(cx, obj);
 
@@ -1217,12 +1217,14 @@ NPObjWrapper_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMut
     if (!ReportExceptionIfPending(cx))
       return JS_FALSE;
 
-    if (!hasProperty)
+    if (!hasProperty) {
+      *succeeded = true;
       return JS_TRUE;
+    }
   }
 
   if (!npobj->_class->removeProperty(npobj, identifier))
-    vp.set(JSVAL_FALSE);
+    *succeeded = false;
 
   return ReportExceptionIfPending(cx);
 }
diff --git a/dom/workers/Events.cpp b/dom/workers/Events.cpp
index 0fb2406ee4a1..8d62b3440a1a 100644
--- a/dom/workers/Events.cpp
+++ b/dom/workers/Events.cpp
@@ -331,7 +331,7 @@ private:
   JSClass _varname = { \
     _name, \
     JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT), \
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub, \
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub, \
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize \
   };
 
@@ -586,7 +586,7 @@ private:
   JSClass _varname = { \
     _name, \
     JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT), \
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub, \
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub, \
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize \
   };
 
@@ -772,7 +772,7 @@ private:
   JSClass _varname = { \
     _name, \
     JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT), \
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub, \
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub, \
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize \
   };
 
@@ -951,7 +951,7 @@ private:
 JSClass ProgressEvent::sClass = {
   "ProgressEvent",
   JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
 };
 
diff --git a/dom/workers/Exceptions.cpp b/dom/workers/Exceptions.cpp
index 9766bb85c9d9..ed212f319a41 100644
--- a/dom/workers/Exceptions.cpp
+++ b/dom/workers/Exceptions.cpp
@@ -157,7 +157,7 @@ private:
 JSClass DOMException::sClass = {
   "DOMException",
   JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
 };
 
diff --git a/dom/workers/File.cpp b/dom/workers/File.cpp
index 047c0ca61cdf..7e59e7e0776f 100644
--- a/dom/workers/File.cpp
+++ b/dom/workers/File.cpp
@@ -203,7 +203,7 @@ private:
 JSClass Blob::sClass = {
   "Blob",
   JSCLASS_HAS_PRIVATE,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
 };
 
@@ -370,7 +370,7 @@ private:
 JSClass File::sClass = {
   "File",
   JSCLASS_HAS_PRIVATE,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
 };
 
diff --git a/dom/workers/ImageData.cpp b/dom/workers/ImageData.cpp
index 90fd6498a968..85d533fab0a2 100644
--- a/dom/workers/ImageData.cpp
+++ b/dom/workers/ImageData.cpp
@@ -135,7 +135,7 @@ private:
 JSClass ImageData::sClass = {
   "ImageData",
   JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
 };
 
diff --git a/dom/workers/Location.cpp b/dom/workers/Location.cpp
index 21bfd098da76..772e8d4214e4 100644
--- a/dom/workers/Location.cpp
+++ b/dom/workers/Location.cpp
@@ -149,7 +149,7 @@ private:
 JSClass Location::sClass = {
   "WorkerLocation",
   JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
 };
 
diff --git a/dom/workers/Navigator.cpp b/dom/workers/Navigator.cpp
index 3e898b84e811..69b45625e5aa 100644
--- a/dom/workers/Navigator.cpp
+++ b/dom/workers/Navigator.cpp
@@ -138,7 +138,7 @@ private:
 JSClass Navigator::sClass = {
   "WorkerNavigator",
   JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
 };
 
diff --git a/dom/workers/Worker.cpp b/dom/workers/Worker.cpp
index 8abc5359fea9..387b3bdfcd8a 100644
--- a/dom/workers/Worker.cpp
+++ b/dom/workers/Worker.cpp
@@ -301,7 +301,7 @@ DOMJSClass Worker::sClass = {
     "Worker",
     JSCLASS_IS_DOMJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(3) |
     JSCLASS_IMPLEMENTS_BARRIERS,
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize,
     NULL, NULL, NULL, NULL, Trace
   },
@@ -321,7 +321,7 @@ DOMIfaceAndProtoJSClass Worker::sProtoClass = {
     "Worker",
     JSCLASS_IS_DOMIFACEANDPROTOJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(2),
     JS_PropertyStub,       /* addProperty */
-    JS_PropertyStub,       /* delProperty */
+    JS_DeletePropertyStub, /* delProperty */
     JS_PropertyStub,       /* getProperty */
     JS_StrictPropertyStub, /* setProperty */
     JS_EnumerateStub,
@@ -464,7 +464,7 @@ DOMJSClass ChromeWorker::sClass = {
   { "ChromeWorker",
     JSCLASS_IS_DOMJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(3) |
     JSCLASS_IMPLEMENTS_BARRIERS,
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize,
     NULL, NULL, NULL, NULL, Trace,
   },
@@ -484,7 +484,7 @@ DOMIfaceAndProtoJSClass ChromeWorker::sProtoClass = {
     "ChromeWorker",
     JSCLASS_IS_DOMIFACEANDPROTOJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(2),
     JS_PropertyStub,       /* addProperty */
-    JS_PropertyStub,       /* delProperty */
+    JS_DeletePropertyStub, /* delProperty */
     JS_PropertyStub,       /* getProperty */
     JS_StrictPropertyStub, /* setProperty */
     JS_EnumerateStub,
diff --git a/dom/workers/WorkerScope.cpp b/dom/workers/WorkerScope.cpp
index e13a1142c8f8..81036b51677f 100644
--- a/dom/workers/WorkerScope.cpp
+++ b/dom/workers/WorkerScope.cpp
@@ -612,7 +612,7 @@ private:
 JSClass WorkerGlobalScope::sClass = {
   "WorkerGlobalScope",
   0,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
@@ -878,7 +878,7 @@ DOMJSClass DedicatedWorkerGlobalScope::sClass = {
     "DedicatedWorkerGlobalScope",
     JSCLASS_DOM_GLOBAL | JSCLASS_IS_DOMJSCLASS | JSCLASS_IMPLEMENTS_BARRIERS |
     JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(3) | JSCLASS_NEW_RESOLVE,
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, reinterpret_cast<JSResolveOp>(Resolve), JS_ConvertStub,
     Finalize, NULL, NULL, NULL, NULL, Trace
   },
@@ -898,7 +898,7 @@ DOMIfaceAndProtoJSClass DedicatedWorkerGlobalScope::sProtoClass = {
     "DedicatedWorkerGlobalScope",
     JSCLASS_IS_DOMIFACEANDPROTOJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(2),
     JS_PropertyStub,       /* addProperty */
-    JS_PropertyStub,       /* delProperty */
+    JS_DeletePropertyStub, /* delProperty */
     JS_PropertyStub,       /* getProperty */
     JS_StrictPropertyStub, /* setProperty */
     JS_EnumerateStub,
diff --git a/js/ipc/ObjectWrapperChild.cpp b/js/ipc/ObjectWrapperChild.cpp
index 7c90e3612cb0..7eb823a5440f 100644
--- a/js/ipc/ObjectWrapperChild.cpp
+++ b/js/ipc/ObjectWrapperChild.cpp
@@ -400,7 +400,7 @@ static const JSClass sCPOW_NewEnumerateState_JSClass = {
     "CPOW NewEnumerate State",
     JSCLASS_HAS_PRIVATE |
     JSCLASS_HAS_RESERVED_SLOTS(sNumNewEnumerateStateSlots),
-    JS_PropertyStub,  JS_PropertyStub,
+    JS_PropertyStub,  JS_DeletePropertyStub,
     JS_PropertyStub,  JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub,
     JS_ConvertStub,   CPOW_NewEnumerateState_Finalize
diff --git a/js/ipc/ObjectWrapperParent.cpp b/js/ipc/ObjectWrapperParent.cpp
index 9a80c99e7690..61a607107328 100644
--- a/js/ipc/ObjectWrapperParent.cpp
+++ b/js/ipc/ObjectWrapperParent.cpp
@@ -274,6 +274,43 @@ ObjectWrapperParent::jsval_from_JSVariant(JSContext* cx, const JSVariant& from,
     }
 }
 
+/*static*/ bool
+ObjectWrapperParent::boolean_from_JSVariant(JSContext* cx, const JSVariant& from,
+                                            JSBool* to)
+{
+    switch (from.type()) {
+    case JSVariant::Tvoid_t:
+        *to = false;
+        return true;
+    case JSVariant::TPObjectWrapperParent: {
+        JS::Rooted<JS::Value> v(cx);
+        if (!jsval_from_PObjectWrapperParent(cx, from.get_PObjectWrapperParent(), v.address()))
+            return false;
+        *to = JS::ToBoolean(v);
+        return true;
+    }
+    case JSVariant::TnsString:
+        {
+            JSString* str = JS_NewUCStringCopyZ(cx, from.get_nsString().BeginReading());
+            if (!str)
+                return false;
+            *to = JS::ToBoolean(JS::StringValue(str));
+            return true;
+        }
+    case JSVariant::Tint:
+        *to = from.get_int() != 0;
+        return true;
+    case JSVariant::Tdouble:
+        *to = JS::ToBoolean(JS::DoubleValue(from.get_double()));
+        return true;
+    case JSVariant::Tbool:
+        *to = from.get_bool();
+        return true;
+    default:
+        return false;
+    }
+}
+
 /*static*/ bool
 ObjectWrapperParent::
 JSObject_to_PObjectWrapperParent(JSContext* cx, JSObject* from, PObjectWrapperParent** to)
@@ -432,7 +469,7 @@ ObjectWrapperParent::CPOW_SetProperty(JSContext *cx, JSHandleObject obj, JSHandl
     
 /*static*/ JSBool
 ObjectWrapperParent::CPOW_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id,
-                                      JSMutableHandleValue vp)
+                                      JSBool *succeeded)
 {
     CPOW_LOG(("Calling CPOW_DelProperty (%s)...",
               JSVAL_TO_CSTR(cx, id)));
@@ -454,7 +491,7 @@ ObjectWrapperParent::CPOW_DelProperty(JSContext *cx, JSHandleObject obj, JSHandl
             self->CallDelProperty(in_id,
                                   aco.StatusPtr(), &out_v) &&
             aco.Ok() &&
-            jsval_from_JSVariant(cx, out_v, vp.address()));
+            boolean_from_JSVariant(cx, out_v, succeeded));
 }
 
 JSBool
@@ -691,4 +728,4 @@ ObjectWrapperParent::CPOW_HasInstance(JSContext *cx, JSHandleObject obj, JSMutab
             self->CallHasInstance(in_v,
                                   aco.StatusPtr(), bp) &&
             aco.Ok());
-}
\ No newline at end of file
+}
diff --git a/js/ipc/ObjectWrapperParent.h b/js/ipc/ObjectWrapperParent.h
index a389b52956d9..89b2e5139a70 100644
--- a/js/ipc/ObjectWrapperParent.h
+++ b/js/ipc/ObjectWrapperParent.h
@@ -63,7 +63,7 @@ private:
     CPOW_AddProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMutableHandleValue vp);
 
     static JSBool
-    CPOW_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMutableHandleValue vp);
+    CPOW_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSBool *succeeded);
 
     static JSBool
     CPOW_GetProperty(JSContext *cx, JSHandleObject obj, JSHandleId id, JSMutableHandleValue vp);
@@ -100,6 +100,8 @@ private:
     static bool jsval_to_JSVariant(JSContext* cx, jsval from, JSVariant* to);
     static bool jsval_from_JSVariant(JSContext* cx, const JSVariant& from,
                                      jsval* to);
+    static bool boolean_from_JSVariant(JSContext* cx, const JSVariant& from,
+                                       JSBool* to);
     static bool
     JSObject_to_PObjectWrapperParent(JSContext* cx, JSObject* from, PObjectWrapperParent** to);
     static bool
diff --git a/js/jsd/jsd_high.cpp b/js/jsd/jsd_high.cpp
index 3a7bea446e36..9ba321cd5e1f 100644
--- a/js/jsd/jsd_high.cpp
+++ b/js/jsd/jsd_high.cpp
@@ -52,7 +52,7 @@ CreateJSDGlobal(JSContext *cx, JSClass *clasp);
 static JSClass global_class = {
     "JSDGlobal", JSCLASS_GLOBAL_FLAGS |
     JSCLASS_HAS_PRIVATE | JSCLASS_PRIVATE_IS_NSISUPPORTS,
-    JS_PropertyStub,  JS_PropertyStub,  JS_PropertyStub,  JS_StrictPropertyStub,
+    JS_PropertyStub,  JS_DeletePropertyStub,  JS_PropertyStub,  JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub,   JS_ConvertStub,   global_finalize
 };
 
diff --git a/js/src/ctypes/CTypes.cpp b/js/src/ctypes/CTypes.cpp
index 4b29ed0ed1e5..e7213fc80c9f 100644
--- a/js/src/ctypes/CTypes.cpp
+++ b/js/src/ctypes/CTypes.cpp
@@ -444,14 +444,14 @@ namespace UInt64 {
 static JSClass sCTypesGlobalClass = {
   "ctypes",
   JSCLASS_HAS_RESERVED_SLOTS(CTYPESGLOBAL_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
 static JSClass sCABIClass = {
   "CABI",
   JSCLASS_HAS_RESERVED_SLOTS(CABI_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
@@ -461,7 +461,7 @@ static JSClass sCABIClass = {
 static JSClass sCTypeProtoClass = {
   "CType",
   JSCLASS_HAS_RESERVED_SLOTS(CTYPEPROTO_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, CType::FinalizeProtoClass,
   NULL, ConstructAbstract, NULL, ConstructAbstract
 };
@@ -471,14 +471,14 @@ static JSClass sCTypeProtoClass = {
 static JSClass sCDataProtoClass = {
   "CData",
   0,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
 static JSClass sCTypeClass = {
   "CType",
   JSCLASS_IMPLEMENTS_BARRIERS | JSCLASS_HAS_RESERVED_SLOTS(CTYPE_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, CType::Finalize,
   NULL, CType::ConstructData, CType::HasInstance, CType::ConstructData,
   CType::Trace
@@ -487,7 +487,7 @@ static JSClass sCTypeClass = {
 static JSClass sCDataClass = {
   "CData",
   JSCLASS_HAS_RESERVED_SLOTS(CDATA_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, ArrayType::Getter, ArrayType::Setter,
+  JS_PropertyStub, JS_DeletePropertyStub, ArrayType::Getter, ArrayType::Setter,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, CData::Finalize,
   NULL, FunctionType::Call, NULL, FunctionType::Call
 };
@@ -495,7 +495,7 @@ static JSClass sCDataClass = {
 static JSClass sCClosureClass = {
   "CClosure",
   JSCLASS_IMPLEMENTS_BARRIERS | JSCLASS_HAS_RESERVED_SLOTS(CCLOSURE_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, CClosure::Finalize,
   NULL, NULL, NULL, NULL, CClosure::Trace
 };
@@ -506,7 +506,7 @@ static JSClass sCClosureClass = {
 static JSClass sCDataFinalizerProtoClass = {
   "CDataFinalizer",
   0,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
@@ -519,7 +519,7 @@ static JSClass sCDataFinalizerProtoClass = {
 static JSClass sCDataFinalizerClass = {
   "CDataFinalizer",
   JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(CDATAFINALIZER_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, CDataFinalizer::Finalize,
 };
 
@@ -679,28 +679,28 @@ static JSFunctionSpec sFunctionInstanceFunctions[] = {
 static JSClass sInt64ProtoClass = {
   "Int64",
   0,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
 static JSClass sUInt64ProtoClass = {
   "UInt64",
   0,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
 static JSClass sInt64Class = {
   "Int64",
   JSCLASS_HAS_RESERVED_SLOTS(INT64_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Int64Base::Finalize
 };
 
 static JSClass sUInt64Class = {
   "UInt64",
   JSCLASS_HAS_RESERVED_SLOTS(INT64_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Int64Base::Finalize
 };
 
diff --git a/js/src/ctypes/Library.cpp b/js/src/ctypes/Library.cpp
index f76221331c25..1c2f8ea7c5ff 100644
--- a/js/src/ctypes/Library.cpp
+++ b/js/src/ctypes/Library.cpp
@@ -33,7 +33,7 @@ typedef Rooted<JSFlatString*>    RootedFlatString;
 static JSClass sLibraryClass = {
   "Library",
   JSCLASS_HAS_RESERVED_SLOTS(LIBRARY_SLOTS),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub,JS_ResolveStub, JS_ConvertStub, Library::Finalize
 };
 
diff --git a/js/xpconnect/idl/nsIXPCScriptable.idl b/js/xpconnect/idl/nsIXPCScriptable.idl
index 569f3ff42082..4315e4dacdcb 100644
--- a/js/xpconnect/idl/nsIXPCScriptable.idl
+++ b/js/xpconnect/idl/nsIXPCScriptable.idl
@@ -19,7 +19,7 @@
  * boolean to PR_TRUE before making the call.  Implementations may skip writing
  * to *_retval unless they want to return PR_FALSE.
  */
-[uuid(1236e34a-21e0-423c-a8c8-9b3f1e6d7060)]
+[uuid(33b9d098-e680-4e4c-88a2-57cccceac145)]
 interface nsIXPCScriptable : nsISupports
 {
     /* bitflags used for 'flags' (only 32 bits available!) */
@@ -84,8 +84,7 @@ interface nsIXPCScriptable : nsISupports
                        in JSValPtr vp);
 
     boolean delProperty(in nsIXPConnectWrappedNative wrapper,
-                       in JSContextPtr cx, in JSObjectPtr obj, in jsid id,
-                       in JSValPtr vp);
+                       in JSContextPtr cx, in JSObjectPtr obj, in jsid id);
 
     // The returnCode should be set to NS_SUCCESS_I_DID_SOMETHING if
     // this method does something.
diff --git a/js/xpconnect/loader/mozJSComponentLoader.cpp b/js/xpconnect/loader/mozJSComponentLoader.cpp
index ae12a414638a..1532b39c8f8a 100644
--- a/js/xpconnect/loader/mozJSComponentLoader.cpp
+++ b/js/xpconnect/loader/mozJSComponentLoader.cpp
@@ -81,7 +81,7 @@ static JSClass kFakeBackstagePassJSClass =
     "FakeBackstagePass",
     0,
     JS_PropertyStub,
-    JS_PropertyStub,
+    JS_DeletePropertyStub,
     JS_PropertyStub,
     JS_StrictPropertyStub,
     JS_EnumerateStub,
diff --git a/js/xpconnect/public/xpc_map_end.h b/js/xpconnect/public/xpc_map_end.h
index 70c40454cb16..d101c87ceafe 100644
--- a/js/xpconnect/public/xpc_map_end.h
+++ b/js/xpconnect/public/xpc_map_end.h
@@ -113,7 +113,7 @@ NS_IMETHODIMP XPC_MAP_CLASSNAME::AddProperty(nsIXPConnectWrappedNative *wrapper,
 #endif
 
 #ifndef XPC_MAP_WANT_DELPROPERTY
-NS_IMETHODIMP XPC_MAP_CLASSNAME::DelProperty(nsIXPConnectWrappedNative *wrapper, JSContext * cx, JSObject * obj, jsid id, jsval * vp, bool *_retval)
+NS_IMETHODIMP XPC_MAP_CLASSNAME::DelProperty(nsIXPConnectWrappedNative *wrapper, JSContext * cx, JSObject * obj, jsid id, bool *_retval)
     {NS_ERROR("never called"); return NS_ERROR_NOT_IMPLEMENTED;}
 #endif
 
diff --git a/js/xpconnect/shell/xpcshell.cpp b/js/xpconnect/shell/xpcshell.cpp
index 767156623aa8..79492ef16c4e 100644
--- a/js/xpconnect/shell/xpcshell.cpp
+++ b/js/xpconnect/shell/xpcshell.cpp
@@ -848,7 +848,7 @@ static JSFunctionSpec glob_functions[] = {
 
 JSClass global_class = {
     "global", 0,
-    JS_PropertyStub,  JS_PropertyStub,  JS_PropertyStub,  JS_StrictPropertyStub,
+    JS_PropertyStub,  JS_DeletePropertyStub,  JS_PropertyStub,  JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub,   JS_ConvertStub,   nullptr
 };
 
@@ -969,7 +969,7 @@ env_resolve(JSContext *cx, JSHandleObject obj, JSHandleId id, unsigned flags,
 
 static JSClass env_class = {
     "environment", JSCLASS_HAS_PRIVATE | JSCLASS_NEW_RESOLVE,
-    JS_PropertyStub,  JS_PropertyStub,
+    JS_PropertyStub,  JS_DeletePropertyStub,
     JS_PropertyStub,  env_setProperty,
     env_enumerate, (JSResolveOp) env_resolve,
     JS_ConvertStub,   nullptr
diff --git a/js/xpconnect/src/XPCComponents.cpp b/js/xpconnect/src/XPCComponents.cpp
index 9fc4e3148208..392f083a5f2d 100644
--- a/js/xpconnect/src/XPCComponents.cpp
+++ b/js/xpconnect/src/XPCComponents.cpp
@@ -2992,7 +2992,7 @@ sandbox_convert(JSContext *cx, JSHandleObject obj, JSType type, JSMutableHandleV
 static JSClass SandboxClass = {
     "Sandbox",
     XPCONNECT_GLOBAL_FLAGS,
-    JS_PropertyStub,   JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub,   JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     sandbox_enumerate, sandbox_resolve, sandbox_convert,  sandbox_finalize,
     NULL, NULL, NULL, NULL, TraceXPCGlobal
 };
diff --git a/js/xpconnect/src/XPCJSContextStack.cpp b/js/xpconnect/src/XPCJSContextStack.cpp
index cab07993ba79..f1d09ba659da 100644
--- a/js/xpconnect/src/XPCJSContextStack.cpp
+++ b/js/xpconnect/src/XPCJSContextStack.cpp
@@ -134,7 +134,7 @@ SafeFinalize(JSFreeOp *fop, JSObject* obj)
 static JSClass global_class = {
     "global_for_XPCJSContextStack_SafeJSContext",
     XPCONNECT_GLOBAL_FLAGS,
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, SafeGlobalResolve, JS_ConvertStub, SafeFinalize,
     NULL, NULL, NULL, NULL, TraceXPCGlobal
 };
diff --git a/js/xpconnect/src/XPCQuickStubs.cpp b/js/xpconnect/src/XPCQuickStubs.cpp
index d734d27a73dd..8432193d51e2 100644
--- a/js/xpconnect/src/XPCQuickStubs.cpp
+++ b/js/xpconnect/src/XPCQuickStubs.cpp
@@ -94,7 +94,7 @@ PointerFinalize(JSFreeOp *fop, JSObject *obj)
 JSClass
 PointerHolderClass = {
     "Pointer", JSCLASS_HAS_PRIVATE,
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, PointerFinalize
 };
 
diff --git a/js/xpconnect/src/XPCWrappedNativeJSOps.cpp b/js/xpconnect/src/XPCWrappedNativeJSOps.cpp
index 35125019ffeb..de781293e608 100644
--- a/js/xpconnect/src/XPCWrappedNativeJSOps.cpp
+++ b/js/xpconnect/src/XPCWrappedNativeJSOps.cpp
@@ -498,6 +498,13 @@ XPC_WN_CannotModifyPropertyStub(JSContext *cx, JSHandleObject obj, JSHandleId id
     return Throw(NS_ERROR_XPC_CANT_MODIFY_PROP_ON_WN, cx);
 }
 
+static JSBool
+XPC_WN_CantDeletePropertyStub(JSContext *cx, JSHandleObject obj, JSHandleId id,
+                              JSBool *succeeded)
+{
+    return Throw(NS_ERROR_XPC_CANT_MODIFY_PROP_ON_WN, cx);
+}
+
 static JSBool
 XPC_WN_CannotModifyStrictPropertyStub(JSContext *cx, JSHandleObject obj, JSHandleId id, JSBool strict,
                                       JSMutableHandleValue vp)
@@ -759,7 +766,7 @@ XPCWrappedNativeJSClass XPC_WN_NoHelper_JSClass = {
 
     /* Mandatory non-null function pointer members. */
     XPC_WN_OnlyIWrite_AddPropertyStub, // addProperty
-    XPC_WN_CannotModifyPropertyStub,   // delProperty
+    XPC_WN_CantDeletePropertyStub,     // delProperty
     JS_PropertyStub,                   // getProperty
     XPC_WN_OnlyIWrite_SetPropertyStub, // setProperty
 
@@ -843,6 +850,21 @@ XPC_WN_MaybeResolvingStrictPropertyStub(JSContext *cx, JSHandleObject obj, JSHan
     return XPC_WN_MaybeResolvingPropertyStub(cx, obj, id, vp);
 }
 
+static JSBool
+XPC_WN_MaybeResolvingDeletePropertyStub(JSContext *cx, JSHandleObject obj, JSHandleId id, JSBool *succeeded)
+{
+    MORPH_SLIM_WRAPPER(cx, obj);
+    XPCCallContext ccx(JS_CALLER, cx, obj);
+    XPCWrappedNative* wrapper = ccx.GetWrapper();
+    THROW_AND_RETURN_IF_BAD_WRAPPER(cx, wrapper);
+
+    if (ccx.GetResolvingWrapper() == wrapper) {
+        *succeeded = true;
+        return true;
+    }
+    return Throw(NS_ERROR_XPC_CANT_MODIFY_PROP_ON_WN, cx);
+}
+
 // macro fun!
 #define PRE_HELPER_STUB_NO_SLIM                                               \
     XPCWrappedNative* wrapper =                                               \
@@ -891,10 +913,10 @@ XPC_WN_Helper_AddProperty(JSContext *cx, JSHandleObject obj, JSHandleId id,
 
 static JSBool
 XPC_WN_Helper_DelProperty(JSContext *cx, JSHandleObject obj, JSHandleId id,
-                          JSMutableHandleValue vp)
+                          JSBool *succeeded)
 {
     PRE_HELPER_STUB
-    DelProperty(wrapper, cx, obj, id, vp.address(), &retval);
+    DelProperty(wrapper, cx, obj, id, &retval);
     POST_HELPER_STUB
 }
 
@@ -1311,15 +1333,15 @@ XPCNativeScriptableShared::PopulateJSClass()
         addProperty = XPC_WN_CannotModifyPropertyStub;
     mJSClass.base.addProperty = addProperty;
 
-    JSPropertyOp delProperty;
+    JSDeletePropertyOp delProperty;
     if (mFlags.WantDelProperty())
         delProperty = XPC_WN_Helper_DelProperty;
     else if (mFlags.UseJSStubForDelProperty())
-        delProperty = JS_PropertyStub;
+        delProperty = JS_DeletePropertyStub;
     else if (mFlags.AllowPropModsDuringResolve())
-        delProperty = XPC_WN_MaybeResolvingPropertyStub;
+        delProperty = XPC_WN_MaybeResolvingDeletePropertyStub;
     else
-        delProperty = XPC_WN_CannotModifyPropertyStub;
+        delProperty = XPC_WN_CantDeletePropertyStub;
     mJSClass.base.delProperty = delProperty;
 
     if (mFlags.WantGetProperty())
@@ -1610,7 +1632,7 @@ js::Class XPC_WN_ModsAllowed_WithCall_Proto_JSClass = {
 
     /* Mandatory non-null function pointer members. */
     JS_PropertyStub,                // addProperty;
-    JS_PropertyStub,                // delProperty;
+    JS_DeletePropertyStub,          // delProperty;
     JS_PropertyStub,                // getProperty;
     JS_StrictPropertyStub,          // setProperty;
     XPC_WN_Shared_Proto_Enumerate,  // enumerate;
@@ -1635,7 +1657,7 @@ js::Class XPC_WN_ModsAllowed_NoCall_Proto_JSClass = {
 
     /* Mandatory non-null function pointer members. */
     JS_PropertyStub,                // addProperty;
-    JS_PropertyStub,                // delProperty;
+    JS_DeletePropertyStub,          // delProperty;
     JS_PropertyStub,                // getProperty;
     JS_StrictPropertyStub,          // setProperty;
     XPC_WN_Shared_Proto_Enumerate,  // enumerate;
@@ -1724,7 +1746,7 @@ js::Class XPC_WN_NoMods_WithCall_Proto_JSClass = {
 
     /* Mandatory non-null function pointer members. */
     XPC_WN_OnlyIWrite_Proto_AddPropertyStub,   // addProperty;
-     XPC_WN_CannotModifyPropertyStub,          // delProperty;
+    XPC_WN_CantDeletePropertyStub,             // delProperty;
     JS_PropertyStub,                           // getProperty;
     XPC_WN_OnlyIWrite_Proto_SetPropertyStub,   // setProperty;
     XPC_WN_Shared_Proto_Enumerate,             // enumerate;
@@ -1749,7 +1771,7 @@ js::Class XPC_WN_NoMods_NoCall_Proto_JSClass = {
 
     /* Mandatory non-null function pointer members. */
     XPC_WN_OnlyIWrite_Proto_AddPropertyStub,   // addProperty;
-    XPC_WN_CannotModifyPropertyStub,           // delProperty;
+    XPC_WN_CantDeletePropertyStub,             // delProperty;
     JS_PropertyStub,                           // getProperty;
     XPC_WN_OnlyIWrite_Proto_SetPropertyStub,   // setProperty;
     XPC_WN_Shared_Proto_Enumerate,             // enumerate;
@@ -1830,7 +1852,7 @@ js::Class XPC_WN_Tearoff_JSClass = {
     WRAPPER_SLOTS,                             // flags;
 
     XPC_WN_OnlyIWrite_AddPropertyStub,         // addProperty;
-    XPC_WN_CannotModifyPropertyStub,           // delProperty;
+    XPC_WN_CantDeletePropertyStub,             // delProperty;
     JS_PropertyStub,                           // getProperty;
     XPC_WN_OnlyIWrite_SetPropertyStub,         // setProperty;
     XPC_WN_TearOff_Enumerate,                  // enumerate;
diff --git a/js/xpconnect/src/XPCWrappedNativeScope.cpp b/js/xpconnect/src/XPCWrappedNativeScope.cpp
index 488b8a4eace3..9593accc82da 100644
--- a/js/xpconnect/src/XPCWrappedNativeScope.cpp
+++ b/js/xpconnect/src/XPCWrappedNativeScope.cpp
@@ -301,7 +301,7 @@ js::Class XPC_WN_NoHelper_Proto_JSClass = {
 
     /* Mandatory non-null function pointer members. */
     JS_PropertyStub,                // addProperty;
-    JS_PropertyStub,                // delProperty;
+    JS_DeletePropertyStub,          // delProperty;
     JS_PropertyStub,                // getProperty;
     JS_StrictPropertyStub,          // setProperty;
     JS_EnumerateStub,               // enumerate;
diff --git a/js/xpconnect/wrappers/XrayWrapper.cpp b/js/xpconnect/wrappers/XrayWrapper.cpp
index b3e6098e1fbf..d76dc37f9a68 100644
--- a/js/xpconnect/wrappers/XrayWrapper.cpp
+++ b/js/xpconnect/wrappers/XrayWrapper.cpp
@@ -42,7 +42,7 @@ namespace XrayUtils {
 JSClass HolderClass = {
     "NativePropertyHolder",
     JSCLASS_HAS_RESERVED_SLOTS(2),
-    JS_PropertyStub,        JS_PropertyStub, holder_get,      holder_set,
+    JS_PropertyStub,        JS_DeletePropertyStub, holder_get,      holder_set,
     JS_EnumerateStub,       JS_ResolveStub,  JS_ConvertStub
 };
 }
@@ -320,7 +320,7 @@ ExpandoObjectFinalize(JSFreeOp *fop, JSObject *obj)
 JSClass ExpandoObjectClass = {
     "XrayExpandoObject",
     JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_EXPANDO_COUNT),
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, ExpandoObjectFinalize
 };
 
diff --git a/netwerk/base/src/ProxyAutoConfig.cpp b/netwerk/base/src/ProxyAutoConfig.cpp
index 5727b39a8891..dec6ca456149 100644
--- a/netwerk/base/src/ProxyAutoConfig.cpp
+++ b/netwerk/base/src/ProxyAutoConfig.cpp
@@ -549,7 +549,7 @@ private:
 JSClass JSRuntimeWrapper::sGlobalClass = {
   "PACResolutionThreadGlobal",
   JSCLASS_GLOBAL_FLAGS,
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+  JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
 };
 
diff --git a/startupcache/test/TestStartupCache.cpp b/startupcache/test/TestStartupCache.cpp
index 1e78ec85263a..c5f07486e971 100644
--- a/startupcache/test/TestStartupCache.cpp
+++ b/startupcache/test/TestStartupCache.cpp
@@ -514,7 +514,7 @@ int main(int argc, char** argv)
   JSAutoRequest req(cx);
   static JSClass global_class = {
     "global", JSCLASS_NEW_RESOLVE | JSCLASS_GLOBAL_FLAGS | JSCLASS_HAS_PRIVATE,
-    JS_PropertyStub,  JS_PropertyStub,
+    JS_PropertyStub,  JS_DeletePropertyStub,
     JS_PropertyStub,  JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub,
     JS_ConvertStub
diff --git a/toolkit/components/telemetry/Telemetry.cpp b/toolkit/components/telemetry/Telemetry.cpp
index c80725fc5234..222c96496660 100644
--- a/toolkit/components/telemetry/Telemetry.cpp
+++ b/toolkit/components/telemetry/Telemetry.cpp
@@ -694,7 +694,7 @@ WrapAndReturnHistogram(Histogram *h, JSContext *cx, JS::Value *ret)
   static JSClass JSHistogram_class = {
     "JSHistogram",  /* name */
     JSCLASS_HAS_PRIVATE, /* flags */
-    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
     JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
   };
 
diff --git a/tools/profiler/SaveProfileTask.h b/tools/profiler/SaveProfileTask.h
index 9e9d4ea561f4..afe8a0f94261 100644
--- a/tools/profiler/SaveProfileTask.h
+++ b/tools/profiler/SaveProfileTask.h
@@ -82,7 +82,7 @@ public:
       JSAutoRequest ar(cx);
       static JSClass c = {
           "global", JSCLASS_GLOBAL_FLAGS,
-          JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+          JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
           JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub
       };
       JSObject *obj = JS_NewGlobalObject(cx, &c, NULL);