diff --git a/js/xpconnect/src/XPCWrappedNativeScope.cpp b/js/xpconnect/src/XPCWrappedNativeScope.cpp
index 40fb4201f7..5c395712fe 100644
--- a/js/xpconnect/src/XPCWrappedNativeScope.cpp
+++ b/js/xpconnect/src/XPCWrappedNativeScope.cpp
@@ -496,22 +496,9 @@ XPCWrappedNativeScope::TraceWrappedNativesInAllScopes(JSTracer* trc, XPCJSContex
             if (wrapper->HasExternalReference() && !wrapper->IsWrapperExpired())
                 wrapper->TraceSelf(trc);
         }
-
-        if (cur->mDOMExpandoSet) {
-            for (DOMExpandoSet::Enum e(*cur->mDOMExpandoSet); !e.empty(); e.popFront())
-                JS::TraceEdge(trc, &e.mutableFront(), "DOM expando object");
-        }
     }
 }
 
-static void
-SuspectDOMExpandos(JSObject* obj, nsCycleCollectionNoteRootCallback& cb)
-{
-    MOZ_ASSERT(dom::GetDOMClass(obj) && dom::GetDOMClass(obj)->mDOMObjectIsISupports);
-    nsISupports* native = dom::UnwrapDOMObject<nsISupports>(obj);
-    cb.NoteXPCOMRoot(native);
-}
-
 // static
 void
 XPCWrappedNativeScope::SuspectAllWrappers(XPCJSContext* cx,
@@ -521,11 +508,6 @@ XPCWrappedNativeScope::SuspectAllWrappers(XPCJSContext* cx,
         for (auto i = cur->mWrappedNativeMap->Iter(); !i.Done(); i.Next()) {
             static_cast<Native2WrappedNativeMap::Entry*>(i.Get())->value->Suspect(cb);
         }
-
-        if (cur->mDOMExpandoSet) {
-            for (DOMExpandoSet::Range r = cur->mDOMExpandoSet->all(); !r.empty(); r.popFront())
-                SuspectDOMExpandos(r.front().unbarrieredGet(), cb);
-        }
     }
 }
 
diff --git a/js/xpconnect/src/xpcprivate.h b/js/xpconnect/src/xpcprivate.h
index 97f5c36fe8..2a773cb4a2 100644
--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -950,28 +950,6 @@ public:
     static bool
     IsDyingScope(XPCWrappedNativeScope* scope);
 
-    typedef js::HashSet<JS::Heap<JSObject*>,
-                        js::MovableCellHasher<JS::Heap<JSObject*>>,
-                        js::SystemAllocPolicy> DOMExpandoSet;
-
-    bool RegisterDOMExpandoObject(JSObject* expando) {
-        // Expandos are proxy objects, and proxies are always tenured.
-        JS::AssertGCThingMustBeTenured(expando);
-        if (!mDOMExpandoSet) {
-            mDOMExpandoSet = new DOMExpandoSet();
-            if (!mDOMExpandoSet->init(8))
-                return false;
-        }
-        return mDOMExpandoSet->put(JS::Heap<JSObject*>(expando));
-    }
-    void RemoveDOMExpandoObject(JSObject* expando) {
-        if (mDOMExpandoSet) {
-            DOMExpandoSet::Ptr p = mDOMExpandoSet->lookup(JS::Heap<JSObject*>(expando));
-            MOZ_ASSERT(p.found());
-            mDOMExpandoSet->remove(p);
-        }
-    }
-
     typedef js::HashMap<JSAddonId*,
                         nsCOMPtr<nsIAddonInterposition>,
                         js::PointerHasher<JSAddonId*, 3>,
@@ -1065,8 +1043,6 @@ private:
     // from this scope if the caller scope has mInterposition set.
     bool mHasCallInterpositions;
 
-    nsAutoPtr<DOMExpandoSet> mDOMExpandoSet;
-
     JS::WeakMapPtr<JSObject*, JSObject*> mXrayExpandos;
 
     bool mIsContentXBLScope;