diff --git a/js/src/gc/Barrier.h b/js/src/gc/Barrier.h
index bc551e9bde0e..08c8de8f0d73 100644
--- a/js/src/gc/Barrier.h
+++ b/js/src/gc/Barrier.h
@@ -303,7 +303,7 @@ struct HeapPtrHasher
 template <class T>
 struct DefaultHasher< HeapPtr<T> > : HeapPtrHasher<T> { };
 
-class EncapsulatedValue
+class EncapsulatedValue : public ValueOperations<EncapsulatedValue>
 {
   protected:
     Value value;
@@ -328,44 +328,20 @@ class EncapsulatedValue
     Value *unsafeGet() { return &value; }
     operator const Value &() const { return value; }
 
-    bool isUndefined() const { return value.isUndefined(); }
-    bool isNull() const { return value.isNull(); }
-    bool isBoolean() const { return value.isBoolean(); }
-    bool isTrue() const { return value.isTrue(); }
-    bool isFalse() const { return value.isFalse(); }
-    bool isNumber() const { return value.isNumber(); }
-    bool isInt32() const { return value.isInt32(); }
-    bool isDouble() const { return value.isDouble(); }
-    bool isString() const { return value.isString(); }
-    bool isObject() const { return value.isObject(); }
-    bool isMagic() const { return value.isMagic(); }
-    bool isMagic(JSWhyMagic why) const { return value.isMagic(why); }
-    bool isGCThing() const { return value.isGCThing(); }
-    bool isMarkable() const { return value.isMarkable(); }
-
-    bool toBoolean() const { return value.toBoolean(); }
-    double toNumber() const { return value.toNumber(); }
-    int32_t toInt32() const { return value.toInt32(); }
-    double toDouble() const { return value.toDouble(); }
-    JSString *toString() const { return value.toString(); }
-    JSObject &toObject() const { return value.toObject(); }
-    JSObject *toObjectOrNull() const { return value.toObjectOrNull(); }
-    void *toGCThing() const { return value.toGCThing(); }
-
     JSGCTraceKind gcKind() const { return value.gcKind(); }
 
     uint64_t asRawBits() const { return value.asRawBits(); }
 
-#ifdef DEBUG
-    JSWhyMagic whyMagic() const { return value.whyMagic(); }
-#endif
-
     static inline void writeBarrierPre(const Value &v);
     static inline void writeBarrierPre(JSCompartment *comp, const Value &v);
 
   protected:
     inline void pre();
     inline void pre(JSCompartment *comp);
+
+  private:
+    friend class ValueOperations<EncapsulatedValue>;
+    const Value * extract() const { return &value; }
 };
 
 class HeapValue : public EncapsulatedValue
diff --git a/js/src/gc/Root.h b/js/src/gc/Root.h
index 6052dd301c12..722088694128 100644
--- a/js/src/gc/Root.h
+++ b/js/src/gc/Root.h
@@ -79,13 +79,19 @@ struct NullPtr
     static void * const constNullValue;
 };
 
+template <typename T>
+class HandleBase {};
+
 /*
  * Reference to a T that has been rooted elsewhere. This is most useful
  * as a parameter type, which guarantees that the T lvalue is properly
  * rooted. See "Move GC Stack Rooting" above.
+ *
+ * If you want to add additional methods to Handle for a specific
+ * specialization, define a HandleBase<T> specialization containing them.
  */
 template <typename T>
-class Handle
+class Handle : public HandleBase<T>
 {
   public:
     /* Creates a handle from a handle of a type convertible to T. */
@@ -139,10 +145,6 @@ class Handle
     void operator =(S v) MOZ_DELETE;
 };
 
-/* Defined in jsapi.h under Value definition */
-template <>
-class Handle<Value>;
-
 typedef Handle<JSObject*>    HandleObject;
 typedef Handle<JSFunction*>  HandleFunction;
 typedef Handle<JSScript*>    HandleScript;
@@ -150,12 +152,19 @@ typedef Handle<JSString*>    HandleString;
 typedef Handle<jsid>         HandleId;
 typedef Handle<Value>        HandleValue;
 
+template <typename T>
+class MutableHandleBase {};
+
 /*
  * Similar to a handle, but the underlying storage can be changed. This is
  * useful for outparams.
+ *
+ * If you want to add additional methods to MutableHandle for a specific
+ * specialization, define a MutableHandleBase<T> specialization containing
+ * them.
  */
 template <typename T>
-class MutableHandle
+class MutableHandle : public MutableHandleBase<T>
 {
   public:
     template <typename S>
@@ -199,13 +208,20 @@ struct RootMethods<T *>
     static bool poisoned(T *v) { return IsPoisonedPtr(v); }
 };
 
+template <typename T>
+class RootedBase {};
+
 /*
  * Local variable of type T whose value is always rooted. This is typically
  * used for local variables, or for non-rooted values being passed to a
  * function that requires a handle, e.g. Foo(Root<T>(cx, x)).
+ *
+ * If you want to add additional methods to MutableHandle for a specific
+ * specialization, define a MutableHandleBase<T> specialization containing
+ * them.
  */
 template <typename T>
-class Rooted
+class Rooted : public RootedBase<T>
 {
     void init(JSContext *cx_)
     {
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 8c65cc908238..23405e0fae20 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -614,75 +614,6 @@ IsPoisonedValue(const Value &v)
 
 /************************************************************************/
 
-/* This is a specialization of the general Handle template in gc/Root.h */
-template <>
-class Handle<Value>
-{
-  public:
-    /*
-     * Construct a handle from an explicitly rooted location. This is the
-     * normal way to create a handle, and normally happens implicitly.
-     */
-    inline Handle(Rooted<Value> &root) {
-        ptr = root.address();
-    }
-
-    /*
-     * This may be called only if the location of the T is guaranteed
-     * to be marked (for some reason other than being a Rooted),
-     * e.g., if it is guaranteed to be reachable from an implicit root.
-     *
-     * Create a Handle from a raw location of a T.
-     */
-    static Handle fromMarkedLocation(const Value *p) {
-        Handle h;
-        h.ptr = p;
-        return h;
-    }
-
-    const Value *address() const { return ptr; }
-    const Value &get() const { return *ptr; }
-    operator const Value &() const { return *ptr; }
-
-    bool operator==(const Handle &h) const { return *ptr == *h.ptr; }
-    bool operator!=(const Handle &h) const { return *ptr != *h.ptr; }
-
-    bool isUndefined() const { return ptr->isUndefined(); }
-    bool isNull() const { return ptr->isNull(); }
-    bool isBoolean() const { return ptr->isBoolean(); }
-    bool isTrue() const { return ptr->isTrue(); }
-    bool isFalse() const { return ptr->isFalse(); }
-    bool isNumber() const { return ptr->isNumber(); }
-    bool isInt32() const { return ptr->isInt32(); }
-    bool isDouble() const { return ptr->isDouble(); }
-    bool isString() const { return ptr->isString(); }
-    bool isObject() const { return ptr->isObject(); }
-    bool isMagic() const { return ptr->isMagic(); }
-    bool isMagic(JSWhyMagic why) const { return ptr->isMagic(why); }
-    bool isGCThing() const { return ptr->isGCThing(); }
-    bool isMarkable() const { return ptr->isMarkable(); }
-
-    bool toBoolean() const { return ptr->toBoolean(); }
-    double toNumber() const { return ptr->toNumber(); }
-    int32_t toInt32() const { return ptr->toInt32(); }
-    double toDouble() const { return ptr->toDouble(); }
-    JSString *toString() const { return ptr->toString(); }
-    JSObject &toObject() const { return ptr->toObject(); }
-    JSObject *toObjectOrNull() const { return ptr->toObjectOrNull(); }
-    void *toGCThing() const { return ptr->toGCThing(); }
-
-#ifdef DEBUG
-    JSWhyMagic whyMagic() const { return ptr->whyMagic(); }
-#endif
-
-  private:
-    Handle() {}
-
-    const Value *ptr;
-};
-
-/************************************************************************/
-
 static JS_ALWAYS_INLINE Value
 NullValue()
 {
@@ -883,6 +814,8 @@ SameType(const Value &lhs, const Value &rhs)
     return JSVAL_SAME_TYPE_IMPL(lhs.data, rhs.data);
 }
 
+/************************************************************************/
+
 template <> struct RootMethods<const Value>
 {
     static Value initial() { return UndefinedValue(); }
@@ -897,6 +830,125 @@ template <> struct RootMethods<Value>
     static bool poisoned(const Value &v) { return IsPoisonedValue(v); }
 };
 
+template <class Outer> class MutableValueOperations;
+
+/*
+ * A class designed for CRTP use in implementing the non-mutating parts of the
+ * Value interface in Value-like classes.  Outer must be a class inheriting
+ * ValueOperations<Outer> with a visible extract() method returning the
+ * const Value* abstracted by Outer.
+ */
+template <class Outer>
+class ValueOperations
+{
+    friend class MutableValueOperations<Outer>;
+    const Value * value() const { return static_cast<const Outer*>(this)->extract(); }
+
+  public:
+    bool isUndefined() const { return value()->isUndefined(); }
+    bool isNull() const { return value()->isNull(); }
+    bool isBoolean() const { return value()->isBoolean(); }
+    bool isTrue() const { return value()->isTrue(); }
+    bool isFalse() const { return value()->isFalse(); }
+    bool isNumber() const { return value()->isNumber(); }
+    bool isInt32() const { return value()->isInt32(); }
+    bool isDouble() const { return value()->isDouble(); }
+    bool isString() const { return value()->isString(); }
+    bool isObject() const { return value()->isObject(); }
+    bool isMagic() const { return value()->isMagic(); }
+    bool isMagic(JSWhyMagic why) const { return value()->isMagic(why); }
+    bool isMarkable() const { return value()->isMarkable(); }
+    bool isPrimitive() const { return value()->isPrimitive(); }
+
+    bool toBoolean() const { return value()->toBoolean(); }
+    double toNumber() const { return value()->toNumber(); }
+    int32_t toInt32() const { return value()->toInt32(); }
+    double toDouble() const { return value()->toDouble(); }
+    JSString *toString() const { return value()->toString(); }
+    JSObject &toObject() const { return value()->toObject(); }
+    JSObject *toObjectOrNull() const { return value()->toObjectOrNull(); }
+    void *toGCThing() const { return value()->toGCThing(); }
+
+#ifdef DEBUG
+    JSWhyMagic whyMagic() const { return value()->whyMagic(); }
+#endif
+};
+
+/*
+ * A class designed for CRTP use in implementing the mutating parts of the
+ * Value interface in Value-like classes.  Outer must be a class inheriting
+ * MutableValueOperations<Outer> with visible extractMutable() and extract()
+ * methods returning the const Value* and Value* abstracted by Outer.
+ */
+template <class Outer>
+class MutableValueOperations : public ValueOperations<Outer>
+{
+    Value * value() { return static_cast<Outer*>(this)->extractMutable(); }
+
+  public:
+    void setNull() { value()->setNull(); }
+    void setUndefined() { value()->setUndefined(); }
+    void setInt32(int32_t i) { value()->setInt32(i); }
+    void setDouble(double d) { value()->setDouble(d); }
+    void setString(JSString *str) { value()->setString(str); }
+    void setString(const JS::Anchor<JSString *> &str) { value()->setString(str); }
+    void setObject(JSObject &obj) { value()->setObject(obj); }
+    void setBoolean(bool b) { value()->setBoolean(b); }
+    void setMagic(JSWhyMagic why) { value()->setMagic(why); }
+    bool setNumber(uint32_t ui) { return value()->setNumber(ui); }
+    bool setNumber(double d) { return value()->setNumber(d); }
+    void setObjectOrNull(JSObject *arg) { value()->setObjectOrNull(); }
+};
+
+/*
+ * Augment the generic Handle<T> interface when T = Value with type-querying
+ * and value-extracting operations.
+ */
+template <>
+class HandleBase<Value> : public ValueOperations<Handle<Value> >
+{
+    friend class ValueOperations<Handle<Value> >;
+    const Value * extract() const {
+        return static_cast<const Handle<Value>*>(this)->address();
+    }
+};
+
+/*
+ * Augment the generic MutableHandle<T> interface when T = Value with
+ * type-querying, value-extracting, and mutating operations.
+ */
+template <>
+class MutableHandleBase<Value> : public MutableValueOperations<MutableHandle<Value> >
+{
+    friend class ValueOperations<Handle<Value> >;
+    const Value * extract() const {
+        return static_cast<const MutableHandle<Value>*>(this)->address();
+    }
+
+    friend class MutableValueOperations<Handle<Value> >;
+    Value * extractMutable() {
+        return static_cast<MutableHandle<Value>*>(this)->address();
+    }
+};
+
+/*
+ * Augment the generic Rooted<T> interface when T = Value with type-querying,
+ * value-extracting, and mutating operations.
+ */
+template <>
+class RootedBase<Value> : public MutableValueOperations<Rooted<Value> >
+{
+    friend class ValueOperations<Rooted<Value> >;
+    const Value * extract() const {
+        return static_cast<const Rooted<Value>*>(this)->address();
+    }
+
+    friend class MutableValueOperations<Handle<Value> >;
+    Value * extractMutable() {
+        return static_cast<Rooted<Value>*>(this)->address();
+    }
+};
+
 /************************************************************************/
 
 #ifndef __GNUC__