--- a/js/xpconnect/src/XPCJSContext.cpp
+++ b/js/xpconnect/src/XPCJSContext.cpp
@@ -785,21 +785,16 @@ XPCJSContext::FinalizeCallback(JSFreeOp*
             self->mGCIsRunning = true;
 
             // We use this occasion to mark and sweep NativeInterfaces,
             // NativeSets, and the WrappedNativeJSClasses...
 
             // Do the marking...
             XPCWrappedNativeScope::MarkAllWrappedNativesAndProtos();
 
-            for (auto i = self->mDetachedWrappedNativeProtoMap->Iter(); !i.Done(); i.Next()) {
-                auto entry = static_cast<XPCWrappedNativeProtoMap::Entry*>(i.Get());
-                static_cast<const XPCWrappedNativeProto*>(entry->key)->Mark();
-            }
-
             // Mark the sets used in the call contexts. There is a small
             // chance that a wrapper's set will change *while* a call is
             // happening which uses that wrapper's old interfface set. So,
             // we need to do this marking to avoid collecting those sets
             // that might no longer be otherwise reachable from the wrappers
             // or the wrapperprotos.
 
             // Skip this part if XPConnect is shutting down. We get into
@@ -1490,25 +1485,16 @@ CompartmentPrivate::SizeOfIncludingThis(
     size_t n = mallocSizeOf(this);
     n += mWrappedJSMap->SizeOfIncludingThis(mallocSizeOf);
     n += mWrappedJSMap->SizeOfWrappedJS(mallocSizeOf);
     return n;
 }
 
 /***************************************************************************/
 
-void XPCJSContext::SystemIsBeingShutDown()
-{
-    for (auto i = mDetachedWrappedNativeProtoMap->Iter(); !i.Done(); i.Next()) {
-        auto entry = static_cast<XPCWrappedNativeProtoMap::Entry*>(i.Get());
-        auto proto = const_cast<XPCWrappedNativeProto*>(static_cast<const XPCWrappedNativeProto*>(entry->key));
-        proto->SystemIsBeingShutDown();
-    }
-}
-
 #define JS_OPTIONS_DOT_STR "javascript.options."
 
 static void
 ReloadPrefsCallback(const char* pref, void* data)
 {
     XPCJSContext* xpccx = reinterpret_cast<XPCJSContext*>(data);
     JSContext* cx = xpccx->Context();
 
@@ -1639,19 +1625,16 @@ XPCJSContext::~XPCJSContext()
     mThisTranslatorMap = nullptr;
 
     delete mNativeScriptableSharedMap;
     mNativeScriptableSharedMap = nullptr;
 
     delete mDyingWrappedNativeProtoMap;
     mDyingWrappedNativeProtoMap = nullptr;
 
-    delete mDetachedWrappedNativeProtoMap;
-    mDetachedWrappedNativeProtoMap = nullptr;
-
 #ifdef MOZ_ENABLE_PROFILER_SPS
     // Tell the profiler that the context is gone
     if (PseudoStack* stack = mozilla_get_pseudo_stack())
         stack->sampleContext(nullptr);
 #endif
 
     Preferences::UnregisterCallback(ReloadPrefsCallback, JS_OPTIONS_DOT_STR, this);
 }
@@ -3313,17 +3296,16 @@ XPCJSContext::XPCJSContext()
    mWrappedJSMap(JSObject2WrappedJSMap::newMap(XPC_JS_MAP_LENGTH)),
    mWrappedJSClassMap(IID2WrappedJSClassMap::newMap(XPC_JS_CLASS_MAP_LENGTH)),
    mIID2NativeInterfaceMap(IID2NativeInterfaceMap::newMap(XPC_NATIVE_INTERFACE_MAP_LENGTH)),
    mClassInfo2NativeSetMap(ClassInfo2NativeSetMap::newMap(XPC_NATIVE_SET_MAP_LENGTH)),
    mNativeSetMap(NativeSetMap::newMap(XPC_NATIVE_SET_MAP_LENGTH)),
    mThisTranslatorMap(IID2ThisTranslatorMap::newMap(XPC_THIS_TRANSLATOR_MAP_LENGTH)),
    mNativeScriptableSharedMap(XPCNativeScriptableSharedMap::newMap(XPC_NATIVE_JSCLASS_MAP_LENGTH)),
    mDyingWrappedNativeProtoMap(XPCWrappedNativeProtoMap::newMap(XPC_DYING_NATIVE_PROTO_MAP_LENGTH)),
-   mDetachedWrappedNativeProtoMap(XPCWrappedNativeProtoMap::newMap(XPC_DETACHED_NATIVE_PROTO_MAP_LENGTH)),
    mGCIsRunning(false),
    mNativesToReleaseArray(),
    mDoingFinalization(false),
    mVariantRoots(nullptr),
    mWrappedJSRoots(nullptr),
    mObjectHolderRoots(nullptr),
    mWatchdogManager(new WatchdogManager(this)),
    mAsyncSnowWhiteFreer(new AsyncFreeSnowWhite()),

--- a/js/xpconnect/src/XPCWrappedNativeProto.cpp
+++ b/js/xpconnect/src/XPCWrappedNativeProto.cpp
@@ -117,17 +117,16 @@ XPCWrappedNativeProto::JSProtoObjectFina
 {
     MOZ_ASSERT(obj == mJSProtoObject, "huh?");
 
     // Only remove this proto from the map if it is the one in the map.
     ClassInfo2WrappedNativeProtoMap* map = GetScope()->GetWrappedNativeProtoMap();
     if (map->Find(mClassInfo) == this)
         map->Remove(mClassInfo);
 
-    GetContext()->GetDetachedWrappedNativeProtoMap()->Remove(this);
     GetContext()->GetDyingWrappedNativeProtoMap()->Add(this);
 
     mJSProtoObject.finalize(js::CastToJSFreeOp(fop)->runtime());
 }
 
 void
 XPCWrappedNativeProto::JSProtoObjectMoved(JSObject* obj, const JSObject* old)
 {

--- a/js/xpconnect/src/nsXPConnect.cpp
+++ b/js/xpconnect/src/nsXPConnect.cpp
@@ -78,17 +78,16 @@ nsXPConnect::~nsXPConnect()
     // we unrooted above), and once after forcing a bunch of shutdown in
     // XPConnect, to clean the stuff we forcibly disconnected. The forced
     // shutdown code defaults to leaking in a number of situations, so we can't
     // get by with only the second GC. :-(
     mContext->GarbageCollect(JS::gcreason::XPCONNECT_SHUTDOWN);
 
     mShuttingDown = true;
     XPCWrappedNativeScope::SystemIsBeingShutDown();
-    mContext->SystemIsBeingShutDown();
 
     // The above causes us to clean up a bunch of XPConnect data structures,
     // after which point we need to GC to clean everything up. We need to do
     // this before deleting the XPCJSContext, because doing so destroys the
     // maps that our finalize callback depends on.
     mContext->GarbageCollect(JS::gcreason::XPCONNECT_SHUTDOWN);
 
     NS_RELEASE(gSystemPrincipal);

--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -173,17 +173,16 @@
 // default initial sizes for maps (hashtables)
 
 #define XPC_JS_MAP_LENGTH                       32
 #define XPC_JS_CLASS_MAP_LENGTH                 32
 
 #define XPC_NATIVE_MAP_LENGTH                    8
 #define XPC_NATIVE_PROTO_MAP_LENGTH              8
 #define XPC_DYING_NATIVE_PROTO_MAP_LENGTH        8
-#define XPC_DETACHED_NATIVE_PROTO_MAP_LENGTH    16
 #define XPC_NATIVE_INTERFACE_MAP_LENGTH         32
 #define XPC_NATIVE_SET_MAP_LENGTH               32
 #define XPC_NATIVE_JSCLASS_MAP_LENGTH           16
 #define XPC_THIS_TRANSLATOR_MAP_LENGTH           4
 #define XPC_WRAPPER_MAP_LENGTH                   8
 
 /***************************************************************************/
 // data declarations...
@@ -450,19 +449,16 @@ public:
         {return mThisTranslatorMap;}
 
     XPCNativeScriptableSharedMap* GetNativeScriptableSharedMap() const
         {return mNativeScriptableSharedMap;}
 
     XPCWrappedNativeProtoMap* GetDyingWrappedNativeProtoMap() const
         {return mDyingWrappedNativeProtoMap;}
 
-    XPCWrappedNativeProtoMap* GetDetachedWrappedNativeProtoMap() const
-        {return mDetachedWrappedNativeProtoMap;}
-
     bool JSContextInitialized(JSContext* cx);
 
     virtual bool
     DescribeCustomObjects(JSObject* aObject, const js::Class* aClasp,
                           char (&aName)[72]) const override;
     virtual bool
     NoteCustomGCThingXPCOMChildren(const js::Class* aClasp, JSObject* aObj,
                                    nsCycleCollectionTraversalCallback& aCb) const override;
@@ -560,18 +556,16 @@ public:
     static void WeakPointerCompartmentCallback(JSContext* cx, JSCompartment* comp, void* data);
 
     inline void AddVariantRoot(XPCTraceableVariant* variant);
     inline void AddWrappedJSRoot(nsXPCWrappedJS* wrappedJS);
     inline void AddObjectHolderRoot(XPCJSObjectHolder* holder);
 
     void DebugDump(int16_t depth);
 
-    void SystemIsBeingShutDown();
-
     bool GCIsRunning() const {return mGCIsRunning;}
 
     ~XPCJSContext();
 
     ShortLivedStringBuffer<nsString> mScratchStrings;
     ShortLivedStringBuffer<nsCString> mScratchCStrings;
 
     void AddGCCallback(xpcGCCallback cb);
@@ -614,17 +608,16 @@ private:
     JSObject2WrappedJSMap*   mWrappedJSMap;
     IID2WrappedJSClassMap*   mWrappedJSClassMap;
     IID2NativeInterfaceMap*  mIID2NativeInterfaceMap;
     ClassInfo2NativeSetMap*  mClassInfo2NativeSetMap;
     NativeSetMap*            mNativeSetMap;
     IID2ThisTranslatorMap*   mThisTranslatorMap;
     XPCNativeScriptableSharedMap* mNativeScriptableSharedMap;
     XPCWrappedNativeProtoMap* mDyingWrappedNativeProtoMap;
-    XPCWrappedNativeProtoMap* mDetachedWrappedNativeProtoMap;
     bool mGCIsRunning;
     nsTArray<nsISupports*> mNativesToReleaseArray;
     bool mDoingFinalization;
     XPCRootSetElem* mVariantRoots;
     XPCRootSetElem* mWrappedJSRoots;
     XPCRootSetElem* mObjectHolderRoots;
     nsTArray<xpcGCCallback> extraGCCallbacks;
     RefPtr<WatchdogManager> mWatchdogManager;