diff --git a/js/ipc/JavaScriptBase.h b/js/ipc/JavaScriptBase.h
index 28db09b557ac..7ed41fe07311 100644
--- a/js/ipc/JavaScriptBase.h
+++ b/js/ipc/JavaScriptBase.h
@@ -111,6 +111,14 @@ class JavaScriptBase : public WrapperOwner, public WrapperAnswer, public Base
         return Answer::AnswerDOMInstanceOf(objId, prototypeID, depth, rs, instanceof);
     }
 
+    bool AnswerIsCallable(const ObjectId &objId, bool *result) {
+        return Answer::AnswerIsCallable(objId, result);
+    }
+
+    bool AnswerIsConstructor(const ObjectId &objId, bool *result) {
+        return Answer::AnswerIsConstructor(objId, result);
+    }
+
     bool RecvDropObject(const ObjectId &objId) {
         return Answer::RecvDropObject(objId);
     }
@@ -196,6 +204,14 @@ class JavaScriptBase : public WrapperOwner, public WrapperAnswer, public Base
         return Base::CallDOMInstanceOf(objId, prototypeID, depth, rs, instanceof);
     }
 
+    bool CallIsCallable(const ObjectId &objId, bool *result) {
+        return Base::CallIsCallable(objId, result);
+    }
+
+    bool CallIsConstructor(const ObjectId &objId, bool *result) {
+        return Base::CallIsConstructor(objId, result);
+    }
+
     /* The following code is needed to suppress a bogus MSVC warning (C4250). */
 
     virtual bool toObjectVariant(JSContext *cx, JSObject *obj, ObjectVariant *objVarp) {
diff --git a/js/ipc/PJavaScript.ipdl b/js/ipc/PJavaScript.ipdl
index 46b4dd4a9b31..9e79afa8a039 100644
--- a/js/ipc/PJavaScript.ipdl
+++ b/js/ipc/PJavaScript.ipdl
@@ -45,6 +45,9 @@ both:
     rpc InstanceOf(uint64_t objId, JSIID iid) returns (ReturnStatus rs, bool instanceof);
     rpc DOMInstanceOf(uint64_t objId, int prototypeID, int depth) returns (ReturnStatus rs, bool instanceof);
 
+    rpc IsCallable(uint64_t objId) returns (bool result);
+    rpc IsConstructor(uint64_t objId) returns (bool result);
+
 parent:
     async __delete__();
 };
diff --git a/js/ipc/WrapperAnswer.cpp b/js/ipc/WrapperAnswer.cpp
index 4f13668d63e2..d6e93c197d83 100644
--- a/js/ipc/WrapperAnswer.cpp
+++ b/js/ipc/WrapperAnswer.cpp
@@ -635,6 +635,47 @@ WrapperAnswer::AnswerDOMInstanceOf(const ObjectId &objId, const int &prototypeID
     return ok(rs);
 }
 
+bool
+WrapperAnswer::AnswerIsCallable(const ObjectId &objId, bool *result)
+{
+    AutoSafeJSContext cx;
+    JSAutoRequest request(cx);
+
+    RootedObject obj(cx, findObjectById(cx, objId));
+    if (!obj) {
+        // This is very unfortunate, but we have no choice.
+        *result = false;
+        return true;
+    }
+    JSAutoCompartment ac(cx, obj); // Not really necessary here, but be safe.
+
+    LOG("%s.isCallable()", ReceiverObj(objId));
+
+    *result = JS::IsCallable(obj);
+    return true;
+}
+
+bool
+WrapperAnswer::AnswerIsConstructor(const ObjectId &objId, bool *result)
+{
+    AutoSafeJSContext cx;
+    JSAutoRequest request(cx);
+
+    RootedObject obj(cx, findObjectById(cx, objId));
+    if (!obj) {
+        // This is very unfortunate, but we have no choice.
+        *result = false;
+        return true;
+    }
+    JSAutoCompartment ac(cx, obj); // Not really necessary here, but be safe.
+
+    LOG("%s.isConstructor()", ReceiverObj(objId));
+
+    *result = JS::IsConstructor(obj);
+    return true;
+}
+
+
 bool
 WrapperAnswer::RecvDropObject(const ObjectId &objId)
 {
diff --git a/js/ipc/WrapperAnswer.h b/js/ipc/WrapperAnswer.h
index e48a4962683d..3f425ce717ed 100644
--- a/js/ipc/WrapperAnswer.h
+++ b/js/ipc/WrapperAnswer.h
@@ -60,6 +60,9 @@ class WrapperAnswer : public virtual JavaScriptShared
     bool AnswerDOMInstanceOf(const ObjectId &objId, const int &prototypeID, const int &depth,
                              ReturnStatus *rs, bool *instanceof);
 
+    bool AnswerIsCallable(const ObjectId &objId, bool *result);
+    bool AnswerIsConstructor(const ObjectId &objId, bool *result);
+
     bool RecvDropObject(const ObjectId &objId);
 
   private:
diff --git a/js/ipc/WrapperOwner.cpp b/js/ipc/WrapperOwner.cpp
index e808745a14de..835866ec0f81 100644
--- a/js/ipc/WrapperOwner.cpp
+++ b/js/ipc/WrapperOwner.cpp
@@ -663,22 +663,49 @@ CPOWProxyHandler::objectMoved(JSObject *proxy, const JSObject *old) const
 }
 
 bool
-CPOWProxyHandler::isCallable(JSObject *obj) const
+CPOWProxyHandler::isCallable(JSObject *proxy) const
 {
-    return OwnerOf(obj)->isCallable(obj);
-}
-
-bool
-CPOWProxyHandler::isConstructor(JSObject *obj) const
-{
-    return isCallable(obj);
+    WrapperOwner *parent = OwnerOf(proxy);
+    if (!parent->active())
+        return false;
+    return parent->isCallable(proxy);
 }
 
 bool
 WrapperOwner::isCallable(JSObject *obj)
 {
     ObjectId objId = idOf(obj);
-    return !!(objId & OBJECT_IS_CALLABLE);
+
+    bool callable = false;
+    if (!CallIsCallable(objId, &callable)) {
+        NS_WARNING("IPC isCallable() failed");
+        return false;
+    }
+
+    return callable;
+}
+
+bool
+CPOWProxyHandler::isConstructor(JSObject *proxy) const
+{
+    WrapperOwner *parent = OwnerOf(proxy);
+    if (!parent->active())
+        return false;
+    return parent->isConstructor(proxy);
+}
+
+bool
+WrapperOwner::isConstructor(JSObject *obj)
+{
+    ObjectId objId = idOf(obj);
+
+    bool constructor = false;
+    if (!CallIsConstructor(objId, &constructor)) {
+        NS_WARNING("IPC isConstructor() failed");
+        return false;
+    }
+
+    return constructor;
 }
 
 void
diff --git a/js/ipc/WrapperOwner.h b/js/ipc/WrapperOwner.h
index e263c86ec459..b70e7446d6c1 100644
--- a/js/ipc/WrapperOwner.h
+++ b/js/ipc/WrapperOwner.h
@@ -61,7 +61,7 @@ class WrapperOwner : public virtual JavaScriptShared
     bool objectClassIs(JSContext *cx, JS::HandleObject obj, js::ESClassValue classValue);
     const char* className(JSContext *cx, JS::HandleObject proxy);
     bool isCallable(JSObject *obj);
-    // isConstructable is implemented here as isCallable.
+    bool isConstructor(JSObject *obj);
 
     nsresult instanceOf(JSObject *obj, const nsID *id, bool *bp);
 
@@ -147,6 +147,9 @@ class WrapperOwner : public virtual JavaScriptShared
                                 ReturnStatus *rs, bool *instanceof) = 0;
     virtual bool CallDOMInstanceOf(const ObjectId &objId, const int &prototypeID, const int &depth,
                                    ReturnStatus *rs, bool *instanceof) = 0;
+
+    virtual bool CallIsCallable(const ObjectId &objId, bool *result) = 0;
+    virtual bool CallIsConstructor(const ObjectId &objId, bool *result) = 0;
 };
 
 bool