diff --git a/js/src/gc/RootMarking.cpp b/js/src/gc/RootMarking.cpp
index 451b346a0e6d..e1bcee128b2f 100644
--- a/js/src/gc/RootMarking.cpp
+++ b/js/src/gc/RootMarking.cpp
@@ -388,11 +388,16 @@ AutoGCRooter::trace(JSTracer *trc)
         return;
       }
 
-      case DESCVECTOR: {
-        AutoPropDescVector::VectorImpl &descriptors =
-            static_cast<AutoPropDescVector *>(this)->vector;
-        for (size_t i = 0, len = descriptors.length(); i < len; i++)
-            descriptors[i].trace(trc);
+      case DESCRIPTORS: {
+        PropDescArray &descriptors =
+            static_cast<AutoPropDescArrayRooter *>(this)->descriptors;
+        for (size_t i = 0, len = descriptors.length(); i < len; i++) {
+            PropDesc &desc = descriptors[i];
+            MarkValueRoot(trc, &desc.pd_, "PropDesc::pd_");
+            MarkValueRoot(trc, &desc.value_, "PropDesc::value_");
+            MarkValueRoot(trc, &desc.get_, "PropDesc::get_");
+            MarkValueRoot(trc, &desc.set_, "PropDesc::set_");
+        }
         return;
       }
 
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index cf1cf71f72c0..7e4176c3a646 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -106,7 +106,7 @@ class JS_PUBLIC_API(AutoGCRooter) {
         PARSER =       -3, /* js::frontend::Parser */
         SHAPEVECTOR =  -4, /* js::AutoShapeVector */
         IDARRAY =      -6, /* js::AutoIdArray */
-        DESCVECTOR =   -7, /* js::AutoPropDescVector */
+        DESCRIPTORS =  -7, /* js::AutoPropDescArrayRooter */
         VALVECTOR =   -10, /* js::AutoValueVector */
         IDVECTOR =    -13, /* js::AutoIdVector */
         OBJVECTOR =   -14, /* js::AutoObjectVector */
diff --git a/js/src/jscompartment.cpp b/js/src/jscompartment.cpp
index 0cbb19d92374..55e8c0b08bad 100644
--- a/js/src/jscompartment.cpp
+++ b/js/src/jscompartment.cpp
@@ -495,41 +495,6 @@ JSCompartment::wrap(JSContext *cx, AutoIdVector &props)
     return true;
 }
 
-bool
-JSCompartment::wrap(JSContext *cx, MutableHandle<PropDesc> desc)
-{
-    if (desc.isUndefined())
-        return true;
-
-    JSCompartment *comp = cx->compartment();
-
-    if (desc.hasValue()) {
-        RootedValue value(cx, desc.value());
-        if (!comp->wrap(cx, &value))
-            return false;
-        desc.setValue(value);
-    }
-    if (desc.hasGet()) {
-        RootedValue get(cx, desc.getterValue());
-        if (!comp->wrap(cx, &get))
-            return false;
-        desc.setGetter(get);
-    }
-    if (desc.hasSet()) {
-        RootedValue set(cx, desc.setterValue());
-        if (!comp->wrap(cx, &set))
-            return false;
-        desc.setSetter(set);
-    }
-    if (desc.descriptorValue().isObject()) {
-        RootedObject descObj(cx, &desc.descriptorValue().toObject());
-        if (!comp->wrap(cx, &descObj))
-            return false;
-        desc.setDescriptorObject(descObj);
-    }
-    return true;
-}
-
 /*
  * This method marks pointers that cross compartment boundaries. It should be
  * called only for per-compartment GCs, since full GCs naturally follow pointers
diff --git a/js/src/jscompartment.h b/js/src/jscompartment.h
index 169e353a2a2c..925968878d17 100644
--- a/js/src/jscompartment.h
+++ b/js/src/jscompartment.h
@@ -318,7 +318,6 @@ struct JSCompartment
     bool wrap(JSContext *cx, js::StrictPropertyOp *op);
     bool wrap(JSContext *cx, JS::MutableHandle<js::PropertyDescriptor> desc);
     bool wrap(JSContext *cx, js::AutoIdVector &props);
-    bool wrap(JSContext *cx, JS::MutableHandle<js::PropDesc> desc);
 
     bool putWrapper(JSContext *cx, const js::CrossCompartmentKey& wrapped, const js::Value& wrapper);
 
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index a0b6670f748f..ced858b44c41 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -268,17 +268,15 @@ js::NewPropertyDescriptorObject(JSContext *cx, Handle<PropertyDescriptor> desc,
     d.initFromPropertyDescriptor(desc);
     if (!d.makeObject(cx))
         return false;
-    vp.set(d.descriptorValue());
+    vp.set(d.pd());
     return true;
 }
 
 void
 PropDesc::initFromPropertyDescriptor(Handle<PropertyDescriptor> desc)
 {
-    MOZ_ASSERT(isUndefined());
-
     isUndefined_ = false;
-    descObj_ = nullptr;
+    pd_.setUndefined();
     attrs = uint8_t(desc.attributes());
     JS_ASSERT_IF(attrs & JSPROP_READONLY, !(attrs & (JSPROP_GETTER | JSPROP_SETTER)));
     if (desc.hasGetterOrSetterObject()) {
@@ -335,7 +333,7 @@ PropDesc::makeObject(JSContext *cx)
         return false;
     }
 
-    descObj_ = obj;
+    pd_.setObject(*obj);
     return true;
 }
 
@@ -435,8 +433,6 @@ HasProperty(JSContext *cx, HandleObject obj, HandleId id, MutableHandleValue vp,
 bool
 PropDesc::initialize(JSContext *cx, const Value &origval, bool checkAccessors)
 {
-    MOZ_ASSERT(isUndefined());
-
     RootedValue v(cx, origval);
 
     /* 8.10.5 step 1 */
@@ -447,7 +443,7 @@ PropDesc::initialize(JSContext *cx, const Value &origval, bool checkAccessors)
     RootedObject desc(cx, &v.toObject());
 
     /* Make a copy of the descriptor. We might need it later. */
-    descObj_ = desc;
+    pd_ = v;
 
     isUndefined_ = false;
 
@@ -539,8 +535,6 @@ PropDesc::initialize(JSContext *cx, const Value &origval, bool checkAccessors)
 void
 PropDesc::complete()
 {
-    MOZ_ASSERT(!isUndefined());
-
     if (isGenericDescriptor() || isDataDescriptor()) {
         if (!hasValue_) {
             hasValue_ = true;
@@ -1054,7 +1048,7 @@ js::DefineProperty(JSContext *cx, HandleObject obj, HandleId id, const PropDesc
          * TrapDefineOwnProperty directly
          */
         if (obj->is<ProxyObject>()) {
-            RootedValue pd(cx, desc.descriptorValue());
+            RootedValue pd(cx, desc.pd());
             return Proxy::defineProperty(cx, obj, id, pd);
         }
         return Reject(cx, obj, JSMSG_OBJECT_NOT_EXTENSIBLE, throwError, rval);
@@ -1096,7 +1090,7 @@ js::DefineOwnProperty(JSContext *cx, HandleObject obj, HandleId id,
 
 bool
 js::ReadPropertyDescriptors(JSContext *cx, HandleObject props, bool checkAccessors,
-                            AutoIdVector *ids, AutoPropDescVector *descs)
+                            AutoIdVector *ids, AutoPropDescArrayRooter *descs)
 {
     if (!GetPropertyNames(cx, props, JSITER_OWNONLY, ids))
         return false;
@@ -1104,11 +1098,11 @@ js::ReadPropertyDescriptors(JSContext *cx, HandleObject props, bool checkAccesso
     RootedId id(cx);
     for (size_t i = 0, len = ids->length(); i < len; i++) {
         id = (*ids)[i];
-        Rooted<PropDesc> desc(cx);
+        PropDesc* desc = descs->append();
         RootedValue v(cx);
-        if (!JSObject::getGeneric(cx, props, props, id, &v) ||
-            !desc.initialize(cx, v, checkAccessors) ||
-            !descs->append(desc))
+        if (!desc ||
+            !JSObject::getGeneric(cx, props, props, id, &v) ||
+            !desc->initialize(cx, v, checkAccessors))
         {
             return false;
         }
@@ -1120,7 +1114,7 @@ bool
 js::DefineProperties(JSContext *cx, HandleObject obj, HandleObject props)
 {
     AutoIdVector ids(cx);
-    AutoPropDescVector descs(cx);
+    AutoPropDescArrayRooter descs(cx);
     if (!ReadPropertyDescriptors(cx, props, true, &ids, &descs))
         return false;
 
@@ -1141,7 +1135,7 @@ js::DefineProperties(JSContext *cx, HandleObject obj, HandleObject props)
          */
         if (obj->is<ProxyObject>()) {
             for (size_t i = 0, len = ids.length(); i < len; i++) {
-                RootedValue pd(cx, descs[i].descriptorValue());
+                RootedValue pd(cx, descs[i].pd());
                 if (!Proxy::defineProperty(cx, obj, ids[i], pd))
                     return false;
             }
diff --git a/js/src/jsobj.h b/js/src/jsobj.h
index e39c53b221b8..35f24f40c067 100644
--- a/js/src/jsobj.h
+++ b/js/src/jsobj.h
@@ -32,7 +32,7 @@ struct ObjectsExtraSizes;
 
 namespace js {
 
-class AutoPropDescVector;
+class AutoPropDescArrayRooter;
 struct GCMarker;
 struct NativeIterator;
 class Nursery;
@@ -1401,7 +1401,7 @@ DefineProperties(JSContext *cx, HandleObject obj, HandleObject props);
  */
 extern bool
 ReadPropertyDescriptors(JSContext *cx, HandleObject props, bool checkAccessors,
-                        AutoIdVector *ids, AutoPropDescVector *descs);
+                        AutoIdVector *ids, AutoPropDescArrayRooter *descs);
 
 /* Read the name using a dynamic lookup on the scopeChain. */
 extern bool
diff --git a/js/src/jsobjinlines.h b/js/src/jsobjinlines.h
index d38692aaaa17..fef7f4a81c76 100644
--- a/js/src/jsobjinlines.h
+++ b/js/src/jsobjinlines.h
@@ -644,7 +644,7 @@ namespace js {
 
 PropDesc::PropDesc(const Value &getter, const Value &setter,
                    Enumerability enumerable, Configurability configurable)
-  : descObj_(nullptr),
+  : pd_(UndefinedValue()),
     value_(UndefinedValue()),
     get_(getter), set_(setter),
     attrs(JSPROP_GETTER | JSPROP_SETTER | JSPROP_SHARED |
@@ -772,17 +772,32 @@ IsInternalFunctionObject(JSObject *funobj)
     return fun->isLambda() && !funobj->getParent();
 }
 
-class AutoPropDescVector : public AutoVectorRooter<PropDesc>
+class AutoPropDescArrayRooter : private AutoGCRooter
 {
   public:
-    explicit AutoPropDescVector(JSContext *cx
-                    MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
-        : AutoVectorRooter<PropDesc>(cx, DESCVECTOR)
-    {
-        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    explicit AutoPropDescArrayRooter(JSContext *cx)
+      : AutoGCRooter(cx, DESCRIPTORS), descriptors(cx)
+    { }
+
+    PropDesc *append() {
+        if (!descriptors.append(PropDesc()))
+            return nullptr;
+        return &descriptors.back();
     }
 
-    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+    bool reserve(size_t n) {
+        return descriptors.reserve(n);
+    }
+
+    PropDesc& operator[](size_t i) {
+        JS_ASSERT(i < descriptors.length());
+        return descriptors[i];
+    }
+
+    friend void AutoGCRooter::trace(JSTracer *trc);
+
+  private:
+    PropDescArray descriptors;
 };
 
 /*
diff --git a/js/src/jsproxy.cpp b/js/src/jsproxy.cpp
index 59e99565e432..53fbd410e3ec 100644
--- a/js/src/jsproxy.cpp
+++ b/js/src/jsproxy.cpp
@@ -1111,7 +1111,7 @@ FromGenericPropertyDescriptor(JSContext *cx, MutableHandle<PropDesc> desc, Mutab
     // steps 3-9
     if (!desc.makeObject(cx))
         return false;
-    rval.set(desc.descriptorValue());
+    rval.set(desc.pd());
     return true;
 }
 
diff --git a/js/src/vm/Debugger.cpp b/js/src/vm/Debugger.cpp
index 68196d0c7f89..409fccc0dab0 100644
--- a/js/src/vm/Debugger.cpp
+++ b/js/src/vm/Debugger.cpp
@@ -809,63 +809,6 @@ Debugger::unwrapDebuggeeValue(JSContext *cx, MutableHandleValue vp)
     return true;
 }
 
-/*
- * Convert Debugger.Objects in desc to debuggee values.
- * Reject non-callable getters and setters.
- */
-static bool
-CheckArgCompartment(JSContext *cx, JSObject *obj, HandleValue v,
-                    const char *methodname, const char *propname)
-{
-    if (v.isObject() && v.toObject().compartment() != obj->compartment()) {
-        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_DEBUG_COMPARTMENT_MISMATCH,
-                             methodname, propname);
-        return false;
-    }
-    return true;
-}
-
-bool
-Debugger::unwrapPropDescInto(JSContext *cx, HandleObject obj, Handle<PropDesc> wrapped,
-                             MutableHandle<PropDesc> unwrapped)
-{
-    MOZ_ASSERT(!wrapped.isUndefined());
-
-    unwrapped.set(wrapped);
-
-    if (unwrapped.hasValue()) {
-        RootedValue value(cx, unwrapped.value());
-        if (!unwrapDebuggeeValue(cx, &value) ||
-            !CheckArgCompartment(cx, obj, value, "defineProperty", "value"))
-        {
-            return false;
-        }
-        unwrapped.setValue(value);
-    }
-
-    if (unwrapped.hasGet()) {
-        RootedValue get(cx, unwrapped.getterValue());
-        if (!unwrapDebuggeeValue(cx, &get) ||
-            !CheckArgCompartment(cx, obj, get, "defineProperty", "get"))
-        {
-            return false;
-        }
-        unwrapped.setGetter(get);
-    }
-
-    if (unwrapped.hasSet()) {
-        RootedValue set(cx, unwrapped.setterValue());
-        if (!unwrapDebuggeeValue(cx, &set) ||
-            !CheckArgCompartment(cx, obj, set, "defineProperty", "set"))
-        {
-            return false;
-        }
-        unwrapped.setSetter(set);
-    }
-
-    return true;
-}
-
 JSTrapStatus
 Debugger::handleUncaughtExceptionHelper(Maybe<AutoCompartment> &ac,
                                         MutableHandleValue *vp, bool callHook)
@@ -5317,26 +5260,24 @@ DebuggerObject_defineProperty(JSContext *cx, unsigned argc, Value *vp)
     Rooted<PropDesc> desc(cx);
     if (!desc.initialize(cx, args[1], false))
         return false;
-    desc.clearDescriptorObject();
+    desc.clearPd();
 
-    if (!dbg->unwrapPropDescInto(cx, obj, desc, &desc))
+    if (!desc.get().unwrapDebuggerObjectsInto(cx, dbg, obj, desc.address()))
         return false;
     if (!desc.checkGetter(cx) || !desc.checkSetter(cx))
         return false;
 
     {
+        RootedId wrappedId(cx);
+
         Maybe<AutoCompartment> ac;
         ac.construct(cx, obj);
-        if (!cx->compartment()->wrapId(cx, id.address()))
-            return false;
-        if (!cx->compartment()->wrap(cx, &desc))
-            return false;
-        if (!desc.makeObject(cx))
+        if (!desc.get().wrapInto(cx, obj, id, wrappedId.address(), desc.address()))
             return false;
 
         ErrorCopier ec(ac, dbg->toJSObject());
         bool dummy;
-        if (!DefineProperty(cx, obj, id, desc, true, &dummy))
+        if (!DefineProperty(cx, obj, wrappedId, desc, true, &dummy))
             return false;
     }
 
@@ -5356,35 +5297,44 @@ DebuggerObject_defineProperties(JSContext *cx, unsigned argc, Value *vp)
         return false;
 
     AutoIdVector ids(cx);
-    AutoPropDescVector descs(cx);
+    AutoPropDescArrayRooter descs(cx);
     if (!ReadPropertyDescriptors(cx, props, false, &ids, &descs))
         return false;
     size_t n = ids.length();
 
+    AutoPropDescArrayRooter unwrappedDescs(cx);
     for (size_t i = 0; i < n; i++) {
-        if (!dbg->unwrapPropDescInto(cx, obj, descs[i], descs[i]))
+        if (!unwrappedDescs.append())
             return false;
-        if (!descs[i].checkGetter(cx) || !descs[i].checkSetter(cx))
+        if (!descs[i].unwrapDebuggerObjectsInto(cx, dbg, obj, &unwrappedDescs[i]))
+            return false;
+        if (!unwrappedDescs[i].checkGetter(cx) || !unwrappedDescs[i].checkSetter(cx))
             return false;
     }
 
     {
+        AutoIdVector rewrappedIds(cx);
+        AutoPropDescArrayRooter rewrappedDescs(cx);
+
         Maybe<AutoCompartment> ac;
         ac.construct(cx, obj);
+        RootedId id(cx);
         for (size_t i = 0; i < n; i++) {
-            if (!cx->compartment()->wrapId(cx, ids[i].address()))
+            if (!rewrappedIds.append(JSID_VOID) || !rewrappedDescs.append())
                 return false;
-            if (!cx->compartment()->wrap(cx, descs[i]))
-                return false;
-            if (descs[i].descriptorValue().isUndefined() && !descs[i].makeObject(cx))
+            id = ids[i];
+            if (!unwrappedDescs[i].wrapInto(cx, obj, id, rewrappedIds[i].address(), &rewrappedDescs[i]))
                 return false;
         }
 
         ErrorCopier ec(ac, dbg->toJSObject());
         for (size_t i = 0; i < n; i++) {
             bool dummy;
-            if (!DefineProperty(cx, obj, ids[i], descs[i], true, &dummy))
+            if (!DefineProperty(cx, obj, rewrappedIds[i],
+                                rewrappedDescs[i], true, &dummy))
+            {
                 return false;
+            }
         }
     }
 
diff --git a/js/src/vm/Debugger.h b/js/src/vm/Debugger.h
index 0bc28b238ea0..df6da16ec406 100644
--- a/js/src/vm/Debugger.h
+++ b/js/src/vm/Debugger.h
@@ -506,8 +506,6 @@ class Debugger : private mozilla::LinkedListElement<Debugger>
      * happens in the target compartment--rotational symmetry.)
      */
     bool unwrapDebuggeeValue(JSContext *cx, MutableHandleValue vp);
-    bool unwrapPropDescInto(JSContext *cx, HandleObject obj, Handle<PropDesc> wrapped,
-                            MutableHandle<PropDesc> unwrapped);
 
     /*
      * Store the Debugger.Frame object for frame in *vp.
diff --git a/js/src/vm/ObjectImpl.cpp b/js/src/vm/ObjectImpl.cpp
index 6c8bdea2d2ac..1538f04af933 100644
--- a/js/src/vm/ObjectImpl.cpp
+++ b/js/src/vm/ObjectImpl.cpp
@@ -18,29 +18,21 @@ using namespace js;
 using JS::GenericNaN;
 
 PropDesc::PropDesc()
+  : pd_(UndefinedValue()),
+    value_(UndefinedValue()),
+    get_(UndefinedValue()),
+    set_(UndefinedValue()),
+    attrs(0),
+    hasGet_(false),
+    hasSet_(false),
+    hasValue_(false),
+    hasWritable_(false),
+    hasEnumerable_(false),
+    hasConfigurable_(false),
+    isUndefined_(true)
 {
-    setUndefined();
 }
 
-void
-PropDesc::setUndefined()
-{
-    descObj_ = nullptr;
-    value_ = UndefinedValue();
-    get_ = UndefinedValue();
-    set_ = UndefinedValue();
-    attrs = 0;
-    hasGet_ = false;
-    hasSet_ = false;
-    hasValue_ = false;
-    hasWritable_ = false;
-    hasEnumerable_ = false;
-    hasConfigurable_ = false;
-
-    isUndefined_ = true;
-}
-
-
 bool
 PropDesc::checkGetter(JSContext *cx)
 {
@@ -67,6 +59,94 @@ PropDesc::checkSetter(JSContext *cx)
     return true;
 }
 
+static bool
+CheckArgCompartment(JSContext *cx, JSObject *obj, HandleValue v,
+                    const char *methodname, const char *propname)
+{
+    if (v.isObject() && v.toObject().compartment() != obj->compartment()) {
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_DEBUG_COMPARTMENT_MISMATCH,
+                             methodname, propname);
+        return false;
+    }
+    return true;
+}
+
+/*
+ * Convert Debugger.Objects in desc to debuggee values.
+ * Reject non-callable getters and setters.
+ */
+bool
+PropDesc::unwrapDebuggerObjectsInto(JSContext *cx, Debugger *dbg, HandleObject obj,
+                                    PropDesc *unwrapped) const
+{
+    MOZ_ASSERT(!isUndefined());
+
+    *unwrapped = *this;
+
+    if (unwrapped->hasValue()) {
+        RootedValue value(cx, unwrapped->value_);
+        if (!dbg->unwrapDebuggeeValue(cx, &value) ||
+            !CheckArgCompartment(cx, obj, value, "defineProperty", "value"))
+        {
+            return false;
+        }
+        unwrapped->value_ = value;
+    }
+
+    if (unwrapped->hasGet()) {
+        RootedValue get(cx, unwrapped->get_);
+        if (!dbg->unwrapDebuggeeValue(cx, &get) ||
+            !CheckArgCompartment(cx, obj, get, "defineProperty", "get"))
+        {
+            return false;
+        }
+        unwrapped->get_ = get;
+    }
+
+    if (unwrapped->hasSet()) {
+        RootedValue set(cx, unwrapped->set_);
+        if (!dbg->unwrapDebuggeeValue(cx, &set) ||
+            !CheckArgCompartment(cx, obj, set, "defineProperty", "set"))
+        {
+            return false;
+        }
+        unwrapped->set_ = set;
+    }
+
+    return true;
+}
+
+/*
+ * Rewrap *idp and the fields of *desc for the current compartment.  Also:
+ * defining a property on a proxy requires pd_ to contain a descriptor object,
+ * so reconstitute desc->pd_ if needed.
+ */
+bool
+PropDesc::wrapInto(JSContext *cx, HandleObject obj, const jsid &id, jsid *wrappedId,
+                   PropDesc *desc) const
+{
+    MOZ_ASSERT(!isUndefined());
+
+    JSCompartment *comp = cx->compartment();
+
+    *wrappedId = id;
+    if (!comp->wrapId(cx, wrappedId))
+        return false;
+
+    *desc = *this;
+    RootedValue value(cx, desc->value_);
+    RootedValue get(cx, desc->get_);
+    RootedValue set(cx, desc->set_);
+
+    if (!comp->wrap(cx, &value) || !comp->wrap(cx, &get) || !comp->wrap(cx, &set))
+        return false;
+
+    desc->value_ = value;
+    desc->get_ = get;
+    desc->set_ = set;
+    return !obj->is<ProxyObject>() || desc->makeObject(cx);
+}
+
 static const ObjectElements emptyElementsHeader(0, 0);
 
 /* Objects with no elements share one empty set of elements. */
@@ -302,7 +382,7 @@ js::ObjectImpl::markChildren(JSTracer *trc)
 void
 PropDesc::trace(JSTracer *trc)
 {
-    gc::MarkObjectRoot(trc, &descObj_, "PropDesc descriptor object");
+    gc::MarkValueRoot(trc, &pd_, "PropDesc pd");
     gc::MarkValueRoot(trc, &value_, "PropDesc value");
     gc::MarkValueRoot(trc, &get_, "PropDesc get");
     gc::MarkValueRoot(trc, &set_, "PropDesc set");
diff --git a/js/src/vm/PropDesc.h b/js/src/vm/PropDesc.h
index b84ea548c786..bea886625635 100644
--- a/js/src/vm/PropDesc.h
+++ b/js/src/vm/PropDesc.h
@@ -12,6 +12,8 @@
 
 namespace js {
 
+class Debugger;
+
 static inline JSPropertyOp
 CastAsPropertyOp(JSObject *object)
 {
@@ -34,7 +36,7 @@ struct PropDesc {
      * Original object from which this descriptor derives, passed through for
      * the benefit of proxies.
      */
-    JSObject *descObj_;
+    Value pd_;
 
     Value value_, get_, set_;
 
@@ -53,7 +55,7 @@ struct PropDesc {
     bool isUndefined_ : 1;
 
     explicit PropDesc(const Value &v)
-      : descObj_(nullptr),
+      : pd_(UndefinedValue()),
         value_(v),
         get_(UndefinedValue()), set_(UndefinedValue()),
         attrs(0),
@@ -64,6 +66,7 @@ struct PropDesc {
     }
 
   public:
+    friend void JS::AutoGCRooter::trace(JSTracer *trc);
     friend struct GCMethods<PropDesc>;
 
     void trace(JSTracer *trc);
@@ -79,7 +82,7 @@ struct PropDesc {
 
     PropDesc(const Value &v, Writability writable,
              Enumerability enumerable, Configurability configurable)
-      : descObj_(nullptr),
+      : pd_(UndefinedValue()),
         value_(v),
         get_(UndefinedValue()), set_(UndefinedValue()),
         attrs((writable ? 0 : JSPROP_READONLY) |
@@ -126,8 +129,8 @@ struct PropDesc {
     void initFromPropertyDescriptor(Handle<JSPropertyDescriptor> desc);
     bool makeObject(JSContext *cx);
 
-    /* Reset the descriptor entirely. */
-    void setUndefined();
+    void setUndefined() { isUndefined_ = true; }
+
     bool isUndefined() const { return isUndefined_; }
 
     bool hasGet() const { MOZ_ASSERT(!isUndefined()); return hasGet_; }
@@ -137,12 +140,8 @@ struct PropDesc {
     bool hasEnumerable() const { MOZ_ASSERT(!isUndefined()); return hasEnumerable_; }
     bool hasConfigurable() const { MOZ_ASSERT(!isUndefined()); return hasConfigurable_; }
 
-    Value descriptorValue() const {
-        MOZ_ASSERT(!isUndefined());
-        return descObj_ ? ObjectValue(*descObj_) : UndefinedValue();
-    }
-    void setDescriptorObject(JSObject *obj) { descObj_ = obj; }
-    void clearDescriptorObject() { setDescriptorObject(nullptr); }
+    Value pd() const { MOZ_ASSERT(!isUndefined()); return pd_; }
+    void clearPd() { pd_ = UndefinedValue(); }
 
     uint8_t attributes() const { MOZ_ASSERT(!isUndefined()); return attrs; }
 
@@ -183,11 +182,6 @@ struct PropDesc {
         MOZ_ASSERT(hasValue());
         return HandleValue::fromMarkedLocation(&value_);
     }
-    void setValue(const Value &value) {
-        MOZ_ASSERT(!isUndefined());
-        value_ = value;
-        hasValue_ = true;
-    }
 
     JSObject * getterObject() const {
         MOZ_ASSERT(!isUndefined());
@@ -211,17 +205,6 @@ struct PropDesc {
         return HandleValue::fromMarkedLocation(&set_);
     }
 
-    void setGetter(const Value &getter) {
-        MOZ_ASSERT(!isUndefined());
-        get_ = getter;
-        hasGet_ = true;
-    }
-    void setSetter(const Value &setter) {
-        MOZ_ASSERT(!isUndefined());
-        set_ = setter;
-        hasSet_ = true;
-    }
-
     /*
      * Unfortunately the values produced by these methods are used such that
      * we can't assert anything here.  :-(
@@ -240,6 +223,12 @@ struct PropDesc {
      */
     bool checkGetter(JSContext *cx);
     bool checkSetter(JSContext *cx);
+
+    bool unwrapDebuggerObjectsInto(JSContext *cx, Debugger *dbg, HandleObject obj,
+                                   PropDesc *unwrapped) const;
+
+    bool wrapInto(JSContext *cx, HandleObject obj, const jsid &id, jsid *wrappedId,
+                  PropDesc *wrappedDesc) const;
 };
 
 } /* namespace js */
@@ -261,7 +250,7 @@ class PropDescOperations
     bool hasEnumerable() const { return desc()->hasEnumerable(); }
     bool hasConfigurable() const { return desc()->hasConfigurable(); }
 
-    Value descriptorValue() const { return desc()->descriptorValue(); }
+    Value pd() const { return desc()->pd(); }
 
     uint8_t attributes() const { return desc()->attributes(); }
 
@@ -280,6 +269,10 @@ class PropDescOperations
 
     JSPropertyOp getter() const { return desc()->getter(); }
     JSStrictPropertyOp setter() const { return desc()->setter(); }
+
+    // We choose not to expose the debugger-specific parts of PropDesc, both
+    // because they are not really general use, but also because they are a
+    // pain to expose.
 };
 
 template <typename Outer>
@@ -306,20 +299,8 @@ class MutablePropDescOperations : public PropDescOperations<Outer>
         return desc()->makeObject(cx);
     }
 
-    void setValue(const Value &value) {
-        desc()->setValue(value);
-    }
-    void setGetter(const Value &getter) {
-        desc()->setGetter(getter);
-    }
-    void setSetter(const Value &setter) {
-        desc()->setSetter(setter);
-    }
-
     void setUndefined() { desc()->setUndefined(); }
-
-    void setDescriptorObject(JSObject *obj) { desc()->setDescriptorObject(obj); }
-    void clearDescriptorObject() { desc()->clearDescriptorObject(); }
+    void clearPd() { desc()->clearPd(); }
 };
 
 } /* namespace JS */
@@ -331,7 +312,8 @@ struct GCMethods<PropDesc> {
     static PropDesc initial() { return PropDesc(); }
     static ThingRootKind kind() { return THING_ROOT_PROP_DESC; }
     static bool poisoned(const PropDesc &desc) {
-        return JS::IsPoisonedPtr(desc.descObj_) ||
+        return (desc.pd_.isGCThing() &&
+                JS::IsPoisonedPtr(desc.pd_.toGCThing())) ||
                (desc.value_.isGCThing() &&
                 JS::IsPoisonedPtr(desc.value_.toGCThing())) ||
                (desc.get_.isGCThing() &&