diff --git a/addon-sdk/source/lib/sdk/util/iteration.js b/addon-sdk/source/lib/sdk/util/iteration.js
index b0ed01e4f0ea..d2750a726f6c 100644
--- a/addon-sdk/source/lib/sdk/util/iteration.js
+++ b/addon-sdk/source/lib/sdk/util/iteration.js
@@ -7,20 +7,9 @@ module.metadata = {
   "stability": "experimental"
 };
 
-// This is known as @@iterator in the ES6 spec.  Until it is bound to
-// some well-known name, find the @@iterator object by expecting it as
-// the first property accessed on a for-of iterable.
-const iteratorSymbol = (function() {
-  try {
-    for (var _ of Proxy.create({get: function(_, name) { throw name; } }))
-      break;
-  } catch (name) {
-    return name;
-  }
-  throw new TypeError;
-})();
-
-exports.iteratorSymbol = iteratorSymbol;
+// Legacy binding for Symbol.iterator. (This export existed before Symbols were
+// implemented in the JS engine.)
+exports.iteratorSymbol = Symbol.iterator;
 
 // An adaptor that, given an object that is iterable with for-of, is
 // suitable for being bound to __iterator__ in order to make the object
diff --git a/browser/components/customizableui/CustomizableUI.jsm b/browser/components/customizableui/CustomizableUI.jsm
index 85727b90afcb..af87bb42cc9d 100644
--- a/browser/components/customizableui/CustomizableUI.jsm
+++ b/browser/components/customizableui/CustomizableUI.jsm
@@ -2662,7 +2662,7 @@ this.CustomizableUI = {
    *     for (let window of CustomizableUI.windows) { ... }
    */
   windows: {
-    "@@iterator": function*() {
+    *[Symbol.iterator]() {
       for (let [window,] of gBuildWindows)
         yield window;
     }
diff --git a/browser/devtools/debugger/debugger-panes.js b/browser/devtools/debugger/debugger-panes.js
index 7c308449f547..511df2c88b1a 100644
--- a/browser/devtools/debugger/debugger-panes.js
+++ b/browser/devtools/debugger/debugger-panes.js
@@ -3261,9 +3261,9 @@ LineResults.prototype = {
 /**
  * A generator-iterator over the global, source or line results.
  */
-GlobalResults.prototype["@@iterator"] =
-SourceResults.prototype["@@iterator"] =
-LineResults.prototype["@@iterator"] = function*() {
+GlobalResults.prototype[Symbol.iterator] =
+SourceResults.prototype[Symbol.iterator] =
+LineResults.prototype[Symbol.iterator] = function*() {
   yield* this._store;
 };
 
diff --git a/browser/devtools/framework/gDevTools.jsm b/browser/devtools/framework/gDevTools.jsm
index 8b5358b0eb83..0b6a0f82161f 100644
--- a/browser/devtools/framework/gDevTools.jsm
+++ b/browser/devtools/framework/gDevTools.jsm
@@ -475,14 +475,14 @@ DevTools.prototype = {
     //   for (let [target, toolbox] of this._toolboxes) toolbox.destroy();
     // Is taken care of by the gDevToolsBrowser.forgetBrowserWindow
   },
+};
 
-  /**
-   * Iterator that yields each of the toolboxes.
-   */
-  '@@iterator': function*() {
-    for (let toolbox of this._toolboxes) {
-      yield toolbox;
-    }
+/**
+ * Iterator that yields each of the toolboxes.
+ */
+Devtools.prototype[Symbol.iterator] = function*() {
+  for (let toolbox of this._toolboxes) {
+    yield toolbox;
   }
 };
 
diff --git a/browser/devtools/shared/widgets/VariablesView.jsm b/browser/devtools/shared/widgets/VariablesView.jsm
index 061faf0b1cfb..cc1d28bcb0fa 100644
--- a/browser/devtools/shared/widgets/VariablesView.jsm
+++ b/browser/devtools/shared/widgets/VariablesView.jsm
@@ -3056,10 +3056,10 @@ Property.prototype = Heritage.extend(Variable.prototype, {
 /**
  * A generator-iterator over the VariablesView, Scopes, Variables and Properties.
  */
-VariablesView.prototype["@@iterator"] =
-Scope.prototype["@@iterator"] =
-Variable.prototype["@@iterator"] =
-Property.prototype["@@iterator"] = function*() {
+VariablesView.prototype[Symbol.iterator] =
+Scope.prototype[Symbol.iterator] =
+Variable.prototype[Symbol.iterator] =
+Property.prototype[Symbol.iterator] = function*() {
   yield* this._store;
 };
 
diff --git a/browser/devtools/shared/widgets/ViewHelpers.jsm b/browser/devtools/shared/widgets/ViewHelpers.jsm
index 68b4be71259d..e3f6c2f88d39 100644
--- a/browser/devtools/shared/widgets/ViewHelpers.jsm
+++ b/browser/devtools/shared/widgets/ViewHelpers.jsm
@@ -1729,7 +1729,7 @@ this.WidgetMethods = {
 /**
  * A generator-iterator over all the items in this container.
  */
-Item.prototype["@@iterator"] =
-WidgetMethods["@@iterator"] = function*() {
+Item.prototype[Symbol.iterator] =
+WidgetMethods[Symbol.iterator] = function*() {
   yield* this._itemsByElement.values();
 };
diff --git a/content/html/content/test/test_formelements.html b/content/html/content/test/test_formelements.html
index b6836314d152..c4714aa6b6f9 100644
--- a/content/html/content/test/test_formelements.html
+++ b/content/html/content/test/test_formelements.html
@@ -32,7 +32,7 @@ names = [];
 for (var name in x) {
   names.push(name);
 }
-is(names.length, 10, "Should have 10 enumerated names");
+is(names.length, 9, "Should have 9 enumerated names");
 is(names[0], "0", "Enum entry 1");
 is(names[1], "1", "Enum entry 2");
 is(names[2], "2", "Enum entry 3");
@@ -41,8 +41,7 @@ is(names[4], "4", "Enum entry 5");
 is(names[5], "something", "Enum entry 6");
 is(names[6], "namedItem", "Enum entry 7");
 is(names[7], "item", "Enum entry 8");
-is(names[8], "@@iterator", "Enum entry 9");
-is(names[9], "length", "Enum entry 10");
+is(names[8], "length", "Enum entry 9");
 
 names = Object.getOwnPropertyNames(x);
 is(names.length, 10, "Should have 10 items");
diff --git a/content/html/content/test/test_htmlcollection.html b/content/html/content/test/test_htmlcollection.html
index e5dd5bfb0e8e..7be164429d48 100644
--- a/content/html/content/test/test_htmlcollection.html
+++ b/content/html/content/test/test_htmlcollection.html
@@ -28,7 +28,7 @@ var names = [];
 for (var name in x) {
   names.push(name);
 }
-is(names.length, 9, "Should have 9 enumerated names");
+is(names.length, 8, "Should have 8 enumerated names");
 is(names[0], "0", "Enum entry 1")
 is(names[1], "1", "Enum entry 2")
 is(names[2], "2", "Enum entry 3")
@@ -36,8 +36,7 @@ is(names[3], "3", "Enum entry 4")
 is(names[4], "something", "Enum entry 5")
 is(names[5], "item", "Enum entry 6")
 is(names[6], "namedItem", "Enum entry 7")
-is(names[7], "@@iterator", "Enum entry 8")
-is(names[8], "length", "Enum entry 9")
+is(names[7], "length", "Enum entry 8")
 
 names = Object.getOwnPropertyNames(x);
 is(names.length, 9, "Should have 9 items");
diff --git a/content/html/content/test/test_named_options.html b/content/html/content/test/test_named_options.html
index 160c0589440d..b6e84a9f2c33 100644
--- a/content/html/content/test/test_named_options.html
+++ b/content/html/content/test/test_named_options.html
@@ -42,7 +42,7 @@ var names2 = [];
 for (var name in opt) {
   names2.push(name);
 }
-is(names2.length, 12, "Should have twelve enumerated names");
+is(names2.length, 11, "Should have eleven enumerated names");
 is(names2[0], "0", "Enum entry 1")
 is(names2[1], "1", "Enum entry 2")
 is(names2[2], "2", "Enum entry 3")
@@ -54,7 +54,6 @@ is(names2[7], "length", "Enum entry 8")
 is(names2[8], "selectedIndex", "Enum entry 9")
 is(names2[9], "item", "Enum entry 10")
 is(names2[10], "namedItem", "Enum entry 11")
-is(names2[11], "@@iterator", "Enum entry 12")
 
 </script>
 </pre>
diff --git a/content/html/content/test/test_rowscollection.html b/content/html/content/test/test_rowscollection.html
index 54483e9e2fc5..6e80e62d4bc3 100644
--- a/content/html/content/test/test_rowscollection.html
+++ b/content/html/content/test/test_rowscollection.html
@@ -38,7 +38,7 @@ var names = [];
 for (var name in x) {
   names.push(name);
 }
-is(names.length, 11, "Should have 11 enumerated names");
+is(names.length, 10, "Should have 10 enumerated names");
 is(names[0], "0", "Enum entry 1")
 is(names[1], "1", "Enum entry 2")
 is(names[2], "2", "Enum entry 3")
@@ -48,8 +48,7 @@ is(names[5], "5", "Enum entry 6")
 is(names[6], "something", "Enum entry 7")
 is(names[7], "item", "Enum entry 8")
 is(names[8], "namedItem", "Enum entry 9")
-is(names[9], "@@iterator", "Enum entry 10")
-is(names[10], "length", "Enum entry 11")
+is(names[9], "length", "Enum entry 10")
 
 names = Object.getOwnPropertyNames(x);
 is(names.length, 11, "Should have 11 items");
diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 7a127de556e2..dd45688ae2e0 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -1942,7 +1942,7 @@ class PropertyDefiner:
                                getAvailableInTestFunc(interfaceMember),
                                descriptor.checkPermissionsIndicesForMembers.get(interfaceMember.identifier.name))
 
-    def generatePrefableArray(self, array, name, specTemplate, specTerminator,
+    def generatePrefableArray(self, array, name, specFormatter, specTerminator,
                               specType, getCondition, getDataTuple, doIdArrays):
         """
         This method generates our various arrays.
@@ -1951,7 +1951,8 @@ class PropertyDefiner:
 
         name is the name as passed to generateArray
 
-        specTemplate is a template for each entry of the spec array
+        specFormatter is a function that takes a single argument, a tuple,
+          and returns a string, a spec array entry
 
         specTerminator is a terminator for the spec array (inserted every time
           our controlling pref changes and at the end of the array)
@@ -1962,7 +1963,7 @@ class PropertyDefiner:
           returns the corresponding MemberCondition.
 
         getDataTuple is a callback function that takes an array entry and
-          returns a tuple suitable for substitution into specTemplate.
+          returns a tuple suitable to be passed to specFormatter.
         """
 
         # We want to generate a single list of specs, but with specTerminator
@@ -2005,7 +2006,7 @@ class PropertyDefiner:
                 switchToCondition(self, curCondition)
                 lastCondition = curCondition
             # And the actual spec
-            specs.append(specTemplate % getDataTuple(member))
+            specs.append(specFormatter(getDataTuple(member)))
         specs.append(specTerminator)
         prefableSpecs.append("  { false, nullptr }")
 
@@ -2279,9 +2280,15 @@ class MethodDefiner(PropertyDefiner):
 
             return (m["name"], accessor, jitinfo, m["length"], flags(m), selfHostedName)
 
+        def formatSpec(fields):
+            if fields[0].startswith("@@"):
+                fields = (fields[0][2:],) + fields[1:]
+                return '  JS_SYM_FNSPEC(%s, %s, %s, %s, %s, %s)' % fields
+            return '  JS_FNSPEC("%s", %s, %s, %s, %s, %s)' % fields
+
         return self.generatePrefableArray(
             array, name,
-            '  JS_FNSPEC("%s", %s, %s, %s, %s, %s)',
+            formatSpec,
             '  JS_FS_END',
             'JSFunctionSpec',
             condition, specData, doIdArrays)
@@ -2384,7 +2391,7 @@ class AttrDefiner(PropertyDefiner):
 
         return self.generatePrefableArray(
             array, name,
-            '  { "%s", %s, %s, %s}',
+            lambda fields: '  { "%s", %s, %s, %s}' % fields,
             '  JS_PS_END',
             'JSPropertySpec',
             PropertyDefiner.getControllingCondition, specData, doIdArrays)
@@ -2412,7 +2419,7 @@ class ConstDefiner(PropertyDefiner):
 
         return self.generatePrefableArray(
             array, name,
-            '  { "%s", %s }',
+            lambda fields: '  { "%s", %s }' % fields,
             '  { 0, JS::UndefinedValue() }',
             'ConstantSpec',
             PropertyDefiner.getControllingCondition, specData, doIdArrays)
diff --git a/js/src/builtin/Array.js b/js/src/builtin/Array.js
index eaaf2c3b0eb2..1b2c365cb725 100644
--- a/js/src/builtin/Array.js
+++ b/js/src/builtin/Array.js
@@ -678,7 +678,7 @@ function ArrayFrom(arrayLike, mapfn=undefined, thisArg=undefined) {
     var attrs = ATTR_CONFIGURABLE | ATTR_ENUMERABLE | ATTR_WRITABLE;
 
     // Steps 6-8.
-    var usingIterator = items["@@iterator"];
+    var usingIterator = items[std_iterator];
     if (usingIterator !== undefined) {
         // Steps 8.a-c.
         var A = IsConstructor(C) ? new C() : [];
diff --git a/js/src/builtin/MapObject.cpp b/js/src/builtin/MapObject.cpp
index 257a97988bfe..156b57444a4c 100644
--- a/js/src/builtin/MapObject.cpp
+++ b/js/src/builtin/MapObject.cpp
@@ -876,7 +876,7 @@ const Class MapIteratorObject::class_ = {
 };
 
 const JSFunctionSpec MapIteratorObject::methods[] = {
-    JS_SELF_HOSTED_FN("@@iterator", "IteratorIdentity", 0, 0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "IteratorIdentity", 0, 0),
     JS_FN("next", next, 0, 0),
     JS_FS_END
 };
@@ -1074,7 +1074,8 @@ MapObject::initClass(JSContext *cx, JSObject *obj)
 
         // Define its alias.
         RootedValue funval(cx, ObjectValue(*fun));
-        if (!JS_DefineProperty(cx, proto, js_std_iterator_str, funval, 0))
+        RootedId iteratorId(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().iterator));
+        if (!JS_DefinePropertyById(cx, proto, iteratorId, funval, 0))
             return nullptr;
     }
     return proto;
@@ -1524,7 +1525,7 @@ const Class SetIteratorObject::class_ = {
 };
 
 const JSFunctionSpec SetIteratorObject::methods[] = {
-    JS_SELF_HOSTED_FN("@@iterator", "IteratorIdentity", 0, 0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "IteratorIdentity", 0, 0),
     JS_FN("next", next, 0, 0),
     JS_FS_END
 };
@@ -1697,7 +1698,8 @@ SetObject::initClass(JSContext *cx, JSObject *obj)
         RootedValue funval(cx, ObjectValue(*fun));
         if (!JS_DefineProperty(cx, proto, "keys", funval, 0))
             return nullptr;
-        if (!JS_DefineProperty(cx, proto, js_std_iterator_str, funval, 0))
+        RootedId iteratorId(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().iterator));
+        if (!JS_DefinePropertyById(cx, proto, iteratorId, funval, 0))
             return nullptr;
     }
     return proto;
diff --git a/js/src/builtin/Utilities.js b/js/src/builtin/Utilities.js
index fae2a5b68650..8d0cc9667181 100644
--- a/js/src/builtin/Utilities.js
+++ b/js/src/builtin/Utilities.js
@@ -83,7 +83,7 @@ var std_WeakMap_clear = WeakMap.prototype.clear;
 var std_WeakMap_delete = WeakMap.prototype.delete;
 var std_Map_has = Map.prototype.has;
 var std_Set_has = Set.prototype.has;
-var std_iterator = '@@iterator'; // FIXME: Change to be a symbol.
+var std_iterator = Symbol.iterator;
 var std_StopIteration = StopIteration;
 var std_Map_iterator = Map.prototype[std_iterator];
 var std_Set_iterator = Set.prototype[std_iterator];
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index deab2d22fc54..db1661c67d27 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -4657,9 +4657,9 @@ EmitIterator(ExclusiveContext *cx, BytecodeEmitter *bce)
     // Convert iterable to iterator.
     if (Emit1(cx, bce, JSOP_DUP) < 0)                          // OBJ OBJ
         return false;
-    if (!EmitAtomOp(cx, cx->names().std_iterator, JSOP_CALLPROP, bce)) // OBJ @@ITERATOR
+    if (Emit2(cx, bce, JSOP_SYMBOL, jsbytecode(JS::SymbolCode::iterator)) < 0) // OBJ OBJ @@ITERATOR
         return false;
-    if (Emit1(cx, bce, JSOP_SWAP) < 0)                         // @@ITERATOR OBJ
+    if (!EmitElemOpBase(cx, bce, JSOP_CALLELEM))               // FN OBJ
         return false;
     if (EmitCall(cx, bce, JSOP_CALL, 0) < 0)                   // ITER
         return false;
@@ -5478,9 +5478,9 @@ EmitYieldStar(ExclusiveContext *cx, BytecodeEmitter *bce, ParseNode *iter)
     // Convert iterable to iterator.
     if (Emit1(cx, bce, JSOP_DUP) < 0)                            // ITERABLE ITERABLE
         return false;
-    if (!EmitAtomOp(cx, cx->names().std_iterator, JSOP_CALLPROP, bce)) // ITERABLE @@ITERATOR
+    if (Emit2(cx, bce, JSOP_SYMBOL, jsbytecode(JS::SymbolCode::iterator)) < 0) // ITERABLE ITERABLE @@ITERATOR
         return false;
-    if (Emit1(cx, bce, JSOP_SWAP) < 0)                           // @@ITERATOR ITERABLE
+    if (!EmitElemOpBase(cx, bce, JSOP_CALLELEM))                 // FN ITERABLE
         return false;
     if (EmitCall(cx, bce, JSOP_CALL, 0, iter) < 0)               // ITER
         return false;
diff --git a/js/src/jit-test/lib/iteration.js b/js/src/jit-test/lib/iteration.js
index 500b28303ec9..04e2495e7260 100644
--- a/js/src/jit-test/lib/iteration.js
+++ b/js/src/jit-test/lib/iteration.js
@@ -5,8 +5,7 @@
 
 load(libdir + "asserts.js");
 
-// FIXME: Import from std::iteration.
-const std_iterator = '@@iterator';
+const std_iterator = Symbol.iterator;
 
 if (typeof assertIteratorResult === 'undefined') {
     var assertIteratorResult = function assertIteratorResult(result, value, done) {
diff --git a/js/src/jit-test/tests/arguments/destructuring-exprbody.js b/js/src/jit-test/tests/arguments/destructuring-exprbody.js
index 81289b92d1c6..7f7bf536a030 100644
--- a/js/src/jit-test/tests/arguments/destructuring-exprbody.js
+++ b/js/src/jit-test/tests/arguments/destructuring-exprbody.js
@@ -1,7 +1,7 @@
 // See bug 763313
 function f([a]) a
 var i = 0;
-var o = {'@@iterator': function () { i++; return {
+var o = {[Symbol.iterator]: function () { i++; return {
   next: function () { i++; return {value: 42, done: false}; }}}};
 assertEq(f(o), 42);
 assertEq(i, 2);
diff --git a/js/src/jit-test/tests/basic/expression-autopsy.js b/js/src/jit-test/tests/basic/expression-autopsy.js
index 26bd4100b42d..ad2985d16adc 100644
--- a/js/src/jit-test/tests/basic/expression-autopsy.js
+++ b/js/src/jit-test/tests/basic/expression-autopsy.js
@@ -109,8 +109,8 @@ check("o[- (o)]");
 // A few one off tests
 check_one("6", (function () { 6() }), " is not a function");
 check_one("Array.prototype.reverse.call(...)", (function () { Array.prototype.reverse.call('123'); }), " is read-only");
-check_one("(intermediate value)['@@iterator'](...).next(...).value", function () { var [{ x }] = [null, {}]; }, " is null");
-check_one("(intermediate value)['@@iterator'](...).next(...).value", function () { ieval("let (x) { var [a, b, [c0, c1]] = [x, x, x]; }") }, " is undefined");
+check_one("(intermediate value)[(intermediate value)](...).next(...).value", function () { var [{ x }] = [null, {}]; }, " is null");
+check_one("(intermediate value)[(intermediate value)](...).next(...).value", function () { ieval("let (x) { var [a, b, [c0, c1]] = [x, x, x]; }") }, " is undefined");
 
 // Check fallback behavior
 assertThrowsInstanceOf(function () { for (let x of undefined) {} }, TypeError);
diff --git a/js/src/jit-test/tests/collections/WeakSet-error.js b/js/src/jit-test/tests/collections/WeakSet-error.js
index 57726671c7d8..a162d3859b22 100644
--- a/js/src/jit-test/tests/collections/WeakSet-error.js
+++ b/js/src/jit-test/tests/collections/WeakSet-error.js
@@ -19,7 +19,7 @@ testMethod("add");
 testMethod("delete");
 testMethod("clear", false);
 
-assertThrowsInstanceOf(function() { new WeakSet({"@@iterator": 2}) }, TypeError);
-assertEq(typeof []["@@iterator"], "function"); // Make sure we fail when @@iterator is removed
+assertThrowsInstanceOf(function() { new WeakSet({[Symbol.iterator]: 2}) }, TypeError);
+assertEq(typeof [][Symbol.iterator], "function");
 
 assertThrowsInstanceOf(function() { WeakSet(); }, TypeError);
diff --git a/js/src/jit-test/tests/collections/iterator-proto-surfaces.js b/js/src/jit-test/tests/collections/iterator-proto-surfaces.js
index 13c52dc8ba05..a0ad0b218b09 100644
--- a/js/src/jit-test/tests/collections/iterator-proto-surfaces.js
+++ b/js/src/jit-test/tests/collections/iterator-proto-surfaces.js
@@ -6,8 +6,8 @@ load(libdir + "iteration.js");
 function test(constructor) {
     var proto = Object.getPrototypeOf(constructor()[std_iterator]());
     var names = Object.getOwnPropertyNames(proto);
-    names.sort();
-    assertDeepEq(names, [std_iterator, 'next']);
+    assertDeepEq(names, ['next']);
+    assertEq(proto.hasOwnProperty(std_iterator), true);
 
     var desc = Object.getOwnPropertyDescriptor(proto, 'next');
     assertEq(desc.configurable, true);
diff --git a/js/src/jit-test/tests/for-of/next-3.js b/js/src/jit-test/tests/for-of/next-3.js
index f0eadc64116a..65661c223525 100644
--- a/js/src/jit-test/tests/for-of/next-3.js
+++ b/js/src/jit-test/tests/for-of/next-3.js
@@ -8,6 +8,6 @@ load(libdir + "asserts.js");
 load(libdir + "iteration.js");
 
 var g = newGlobal();
-g.eval("var it = [1, 2]['" + std_iterator + "']();");
+g.eval("var it = [1, 2][Symbol.iterator]();");
 assertIteratorNext(g.it, 1);
 assertThrowsInstanceOf([][std_iterator]().next.bind(g.it), TypeError)
diff --git a/js/src/jit-test/tests/for-of/semantics-08.js b/js/src/jit-test/tests/for-of/semantics-08.js
index 9c0cc08ea994..0bb801e56a13 100644
--- a/js/src/jit-test/tests/for-of/semantics-08.js
+++ b/js/src/jit-test/tests/for-of/semantics-08.js
@@ -3,7 +3,8 @@
 load(libdir + "iteration.js");
 
 var g = newGlobal();
-var it = g.eval("({ '" + std_iterator + "': function () { return this; }, " +
-                "next: function () { return { done: true } } });");
-for (x of it)
+g.eval("var obj = {};\n" +
+       "obj[Symbol.iterator] = function () { return this; };\n" +
+       "obj.next = function () { return { done: true }; };\n");
+for (x of g.obj)
     throw 'FAIL';
diff --git a/js/src/jit-test/tests/for-of/string-iterator-surfaces.js b/js/src/jit-test/tests/for-of/string-iterator-surfaces.js
index 81e5fd841f1c..dee308792ff7 100644
--- a/js/src/jit-test/tests/for-of/string-iterator-surfaces.js
+++ b/js/src/jit-test/tests/for-of/string-iterator-surfaces.js
@@ -57,7 +57,8 @@ var iterProto = Object.getPrototypeOf(iter);
 assertEq(Object.getPrototypeOf(iterProto), Object.prototype);
 
 // Own properties for StringIterator.prototype: "next" and @@iterator
-arraysEqual(Object.getOwnPropertyNames(iterProto).sort(), ["next", std_iterator].sort());
+arraysEqual(Object.getOwnPropertyNames(iterProto), ["next"]);
+assertEq(iterProto.hasOwnProperty(std_iterator), true);
 
 // StringIterator.prototype[@@iterator] is a built-in function
 assertBuiltinFunction(iterProto, std_iterator, 0);
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 4c87931504a4..3941e9e9463a 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -5618,7 +5618,7 @@ JS::GetSymbolCode(Handle<Symbol*> symbol)
 JS_PUBLIC_API(JS::Symbol *)
 JS::GetWellKnownSymbol(JSContext *cx, JS::SymbolCode which)
 {
-    return cx->runtime()->wellKnownSymbols->get(uint32_t(which));
+    return cx->wellKnownSymbols().get(uint32_t(which));
 }
 
 JS_PUBLIC_API(bool)
diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
index a191279f2b77..ff895b1e6e0b 100644
--- a/js/src/jsarray.cpp
+++ b/js/src/jsarray.cpp
@@ -3020,7 +3020,7 @@ static const JSFunctionSpec array_methods[] = {
 
     JS_SELF_HOSTED_FN("fill",        "ArrayFill",        3,0),
 
-    JS_SELF_HOSTED_FN("@@iterator",  "ArrayValues",      0,0),
+    JS_SELF_HOSTED_SYM_FN(iterator,  "ArrayValues",      0,0),
     JS_SELF_HOSTED_FN("entries",     "ArrayEntries",     0,0),
     JS_SELF_HOSTED_FN("keys",        "ArrayKeys",        0,0),
     JS_FS_END
diff --git a/js/src/jsiter.cpp b/js/src/jsiter.cpp
index 4ed25f630808..7e26ce4a560a 100644
--- a/js/src/jsiter.cpp
+++ b/js/src/jsiter.cpp
@@ -885,7 +885,7 @@ iterator_next(JSContext *cx, unsigned argc, Value *vp)
 }
 
 static const JSFunctionSpec iterator_methods[] = {
-    JS_SELF_HOSTED_FN("@@iterator", "LegacyIteratorShim", 0, 0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "LegacyIteratorShim", 0, 0),
     JS_FN("next",      iterator_next,       0, 0),
     JS_FS_END
 };
@@ -964,7 +964,7 @@ const Class ArrayIteratorObject::class_ = {
 };
 
 static const JSFunctionSpec array_iterator_methods[] = {
-    JS_SELF_HOSTED_FN("@@iterator", "ArrayIteratorIdentity", 0, 0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "ArrayIteratorIdentity", 0, 0),
     JS_SELF_HOSTED_FN("next", "ArrayIteratorNext", 0, 0),
     JS_FS_END
 };
@@ -1003,7 +1003,7 @@ const Class StringIteratorObject::class_ = {
 };
 
 static const JSFunctionSpec string_iterator_methods[] = {
-    JS_SELF_HOSTED_FN("@@iterator", "StringIteratorIdentity", 0, 0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "StringIteratorIdentity", 0, 0),
     JS_SELF_HOSTED_FN("next", "StringIteratorNext", 0, 0),
     JS_FS_END
 };
@@ -1405,7 +1405,8 @@ ForOfIterator::init(HandleValue iterable, NonIterableBehavior nonIterableBehavio
     args.setThis(ObjectValue(*iterableObj));
 
     RootedValue callee(cx);
-    if (!JSObject::getProperty(cx, iterableObj, iterableObj, cx->names().std_iterator, &callee))
+    RootedId iteratorId(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().iterator));
+    if (!JSObject::getGeneric(cx, iterableObj, iterableObj, iteratorId, &callee))
         return false;
 
     // Throw if obj[@@iterator] isn't callable if we were asked to do so.
@@ -2014,14 +2015,14 @@ NativeMethod(JSContext *cx, unsigned argc, Value *vp)
 #define JS_METHOD(name, T, impl, len, attrs) JS_FN(name, (NativeMethod<T,impl>), len, attrs)
 
 static const JSFunctionSpec star_generator_methods[] = {
-    JS_SELF_HOSTED_FN("@@iterator", "IteratorIdentity", 0, 0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "IteratorIdentity", 0, 0),
     JS_METHOD("next", StarGeneratorObject, star_generator_next, 1, 0),
     JS_METHOD("throw", StarGeneratorObject, star_generator_throw, 1, 0),
     JS_FS_END
 };
 
 static const JSFunctionSpec legacy_generator_methods[] = {
-    JS_SELF_HOSTED_FN("@@iterator", "LegacyGeneratorIteratorShim", 0, 0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "LegacyGeneratorIteratorShim", 0, 0),
     // "send" is an alias for "next".
     JS_METHOD("next", LegacyGeneratorObject, legacy_generator_next, 1, JSPROP_ROPERM),
     JS_METHOD("send", LegacyGeneratorObject, legacy_generator_next, 1, JSPROP_ROPERM),
diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index b9ebfba31e94..9c6d7c64b14c 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -4200,7 +4200,7 @@ static const JSFunctionSpec string_methods[] = {
     JS_SELF_HOSTED_FN("fontcolor","String_fontcolor",  1,0),
     JS_SELF_HOSTED_FN("fontsize", "String_fontsize",   1,0),
 
-    JS_SELF_HOSTED_FN("@@iterator", "String_iterator", 0,0),
+    JS_SELF_HOSTED_SYM_FN(iterator, "String_iterator", 0,0),
     JS_FS_END
 };
 
diff --git a/js/src/tests/ecma_6/Array/for_of_2.js b/js/src/tests/ecma_6/Array/for_of_2.js
index 8d72fb7b50bb..1d5dd81fc616 100644
--- a/js/src/tests/ecma_6/Array/for_of_2.js
+++ b/js/src/tests/ecma_6/Array/for_of_2.js
@@ -25,7 +25,7 @@ function TestChangeArrayIteratorNext() {
         return M2;
     }
 
-    var iter = ([])['@@iterator']();
+    var iter = ([])[Symbol.iterator]();
     var iterProto = Object.getPrototypeOf(iter);
     var OldNext = iterProto.next;
     var NewNext = function () {
diff --git a/js/src/tests/ecma_6/Array/for_of_3.js b/js/src/tests/ecma_6/Array/for_of_3.js
index 9895da2f00a1..c90eb1f000ba 100644
--- a/js/src/tests/ecma_6/Array/for_of_3.js
+++ b/js/src/tests/ecma_6/Array/for_of_3.js
@@ -27,7 +27,7 @@ function TestIncreaseArrayLength() {
         return M2;
     }
 
-    var iter = ([])['@@iterator']();
+    var iter = ([])[Symbol.iterator]();
     var iterProto = Object.getPrototypeOf(iter);
     var OldNext = iterProto.next;
     var NewNext = function () {
diff --git a/js/src/tests/ecma_6/Array/for_of_4.js b/js/src/tests/ecma_6/Array/for_of_4.js
index 1596038839d4..4572727a1fd3 100644
--- a/js/src/tests/ecma_6/Array/for_of_4.js
+++ b/js/src/tests/ecma_6/Array/for_of_4.js
@@ -26,7 +26,7 @@ function TestDecreaseArrayLength() {
         return M2;
     }
 
-    var iter = ([])['@@iterator']();
+    var iter = ([])[Symbol.iterator]();
     var iterProto = Object.getPrototypeOf(iter);
     var OldNext = iterProto.next;
     var NewNext = function () {
diff --git a/js/src/tests/ecma_6/Array/from_errors.js b/js/src/tests/ecma_6/Array/from_errors.js
index ad494a3507c0..0bc08744b15a 100644
--- a/js/src/tests/ecma_6/Array/from_errors.js
+++ b/js/src/tests/ecma_6/Array/from_errors.js
@@ -132,12 +132,12 @@ assertEq(obj instanceof C, true);
 
 // It's a TypeError if the iterator's .next() method returns a primitive.
 for (var primitive of [undefined, null, 17]) {
+    var iterable = {};
+    iterable[Symbol.iterator] = () => {
+        next: () => primitive
+    };
     assertThrowsInstanceOf(
-        () => Array.from({
-            "@@iterator": () => {
-                next: () => primitive
-            }
-        }),
+        () => Array.from(iterable),
         TypeError);
 }
 
diff --git a/js/src/tests/ecma_6/Array/from_iterable.js b/js/src/tests/ecma_6/Array/from_iterable.js
index 2fe3f890ad44..568181961271 100644
--- a/js/src/tests/ecma_6/Array/from_iterable.js
+++ b/js/src/tests/ecma_6/Array/from_iterable.js
@@ -8,7 +8,7 @@
 
 // If an object has both .length and [@@iterator] properties, [@@iterator] is used.
 var a = ['a', 'e', 'i', 'o', 'u'];
-a["@@iterator"] = function* () {
+a[Symbol.iterator] = function* () {
     for (var i = 5; i--; )
         yield this[i];
 };
diff --git a/js/src/tests/ecma_6/Array/from_proxy.js b/js/src/tests/ecma_6/Array/from_proxy.js
index 40505e8a83e9..5a5cc5b93711 100644
--- a/js/src/tests/ecma_6/Array/from_proxy.js
+++ b/js/src/tests/ecma_6/Array/from_proxy.js
@@ -6,19 +6,19 @@ var log = [];
 function LoggingProxy(target) {
     var h = {
         defineProperty: function (t, id) {
-            log.push("define " + id);
+            log.push("define", id);
             return undefined;
         },
         has: function (t, id) {
-            log.push("has " + id);
+            log.push("has", id);
             return id in t;
         },
         get: function (t, id) {
-            log.push("get " + id);
+            log.push("get", id);
             return t[id];
         },
         set: function (t, id, v) {
-            log.push("set " + id);
+            log.push("set", id);
             t[id] = v;
         }
     };
@@ -30,23 +30,25 @@ function LoggingProxy(target) {
 // but handler.set to set the length.
 LoggingProxy.from = Array.from;
 LoggingProxy.from([3, 4, 5]);
-assertDeepEq(log, ["define 0", "define 1", "define 2", "set length"]);
+assertDeepEq(log, ["define", "0", "define", "1", "define", "2", "set", "length"]);
 
 // When the argument passed to Array.from is a Proxy, Array.from
 // calls handler.get on it.
 log = [];
 assertDeepEq(Array.from(new LoggingProxy([3, 4, 5])), [3, 4, 5]);
-assertDeepEq(log, ["get @@iterator",
-                   "get length", "get 0", "get length", "get 1", "get length", "get 2",
-                   "get length"]);
+assertDeepEq(log, ["get", Symbol.iterator,
+                   "get", "length", "get", "0",
+                   "get", "length", "get", "1",
+                   "get", "length", "get", "2",
+                   "get", "length"]);
 
 // Array-like iteration only gets the length once.
 log = [];
 var arr = [5, 6, 7];
-arr["@@iterator"] = undefined;
+arr[Symbol.iterator] = undefined;
 assertDeepEq(Array.from(new LoggingProxy(arr)), [5, 6, 7]);
-assertDeepEq(log, ["get @@iterator",
-                   "get length", "get 0", "get 1", "get 2"]);
+assertDeepEq(log, ["get", Symbol.iterator,
+                   "get", "length", "get", "0", "get", "1", "get", "2"]);
 
 if (typeof reportCompare === 'function')
     reportCompare(0, 0);
diff --git a/js/src/tests/ecma_6/Array/from_string.js b/js/src/tests/ecma_6/Array/from_string.js
index 892954621789..3ad19e253a68 100644
--- a/js/src/tests/ecma_6/Array/from_string.js
+++ b/js/src/tests/ecma_6/Array/from_string.js
@@ -11,11 +11,11 @@ assertDeepEq(Array.from(gclef), [gclef]);
 assertDeepEq(Array.from(gclef + " G"), [gclef, " ", "G"]);
 
 // Array.from on a string calls the @@iterator method.
-String.prototype["@@iterator"] = function* () { yield 1; yield 2; };
+String.prototype[Symbol.iterator] = function* () { yield 1; yield 2; };
 assertDeepEq(Array.from("anything"), [1, 2]);
 
 // If the iterator method is deleted, Strings are still arraylike.
-delete String.prototype["@@iterator"];
+delete String.prototype[Symbol.iterator];
 assertDeepEq(Array.from("works"), ['w', 'o', 'r', 'k', 's']);
 assertDeepEq(Array.from(gclef), ['\uD834', '\uDD1E']);
 
diff --git a/js/src/tests/ecma_6/Generators/runtime.js b/js/src/tests/ecma_6/Generators/runtime.js
index 4c4ece9c3b84..2c69a5c7e320 100644
--- a/js/src/tests/ecma_6/Generators/runtime.js
+++ b/js/src/tests/ecma_6/Generators/runtime.js
@@ -17,8 +17,6 @@ function* g() { yield 1; }
 var GeneratorFunctionPrototype = Object.getPrototypeOf(g);
 var GeneratorFunction = GeneratorFunctionPrototype.constructor;
 var GeneratorObjectPrototype = GeneratorFunctionPrototype.prototype;
-// FIXME: This should be a symbol.
-var std_iterator = "@@iterator";
 
 
 // A generator function should have the same set of properties as any
@@ -66,7 +64,7 @@ function TestGeneratorObjectPrototype() {
     assertEq(Object.getPrototypeOf((function*(){yield 1}).prototype),
                GeneratorObjectPrototype);
 
-    var expected_property_names = ["next", "throw", "constructor", std_iterator];
+    var expected_property_names = ["next", "throw", "constructor"];
     var found_property_names =
         Object.getOwnPropertyNames(GeneratorObjectPrototype);
 
diff --git a/js/src/tests/ecma_6/Symbol/property-reflection.js b/js/src/tests/ecma_6/Symbol/property-reflection.js
index c7e30ddb4d4e..43bd5dffdb38 100644
--- a/js/src/tests/ecma_6/Symbol/property-reflection.js
+++ b/js/src/tests/ecma_6/Symbol/property-reflection.js
@@ -67,9 +67,7 @@ if (typeof Symbol === "function") {
     assertEq(descs.hasOwnProperty(s2), true);
     assertEq(descs.hasOwnProperty(s3), false);
     assertEq([].hasOwnProperty(Symbol.iterator), false);
-    if (!("@@iterator" in []))
-        throw new Error("Congratulations on implementing Symbol.iterator! Please update this test.");
-    assertEq(Array.prototype.hasOwnProperty(Symbol.iterator), false);  // should be true
+    assertEq(Array.prototype.hasOwnProperty(Symbol.iterator), true);
 
     // Object.prototype.propertyIsEnumerable
     assertEq(n.propertyIsEnumerable(s1), true);
diff --git a/js/src/tests/js1_8/regress/regress-469625-03.js b/js/src/tests/js1_8/regress/regress-469625-03.js
index e48034f6a5cc..2c3047bc92b1 100644
--- a/js/src/tests/js1_8/regress/regress-469625-03.js
+++ b/js/src/tests/js1_8/regress/regress-469625-03.js
@@ -26,7 +26,7 @@ function test()
     var [a, b, [c0, c1]] = [x, x, x];
   }
 
-  expect = 'TypeError: (intermediate value)[\'@@iterator\'](...).next(...).value is null';
+  expect = 'TypeError: (intermediate value)[(intermediate value)](...).next(...).value is null';
   actual = 'No Error';
   try
   {
diff --git a/js/src/vm/CommonPropertyNames.h b/js/src/vm/CommonPropertyNames.h
index a5f3aaf97233..a24ab0c89876 100644
--- a/js/src/vm/CommonPropertyNames.h
+++ b/js/src/vm/CommonPropertyNames.h
@@ -44,7 +44,6 @@
     macro(count, count, "count") \
     macro(currency, currency, "currency") \
     macro(currencyDisplay, currencyDisplay, "currencyDisplay") \
-    macro(std_iterator, std_iterator, "@@iterator") \
     macro(DateTimeFormat, DateTimeFormat, "DateTimeFormat") \
     macro(DateTimeFormatFormatGet, DateTimeFormatFormatGet, "Intl_DateTimeFormat_format_get") \
     macro(decodeURI, decodeURI, "decodeURI") \
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index 2216b6bdd566..d683f54ddae5 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -1133,6 +1133,7 @@ HandleError(JSContext *cx, InterpreterRegs &regs)
 #define PUSH_BOOLEAN(b)          REGS.sp++->setBoolean(b)
 #define PUSH_DOUBLE(d)           REGS.sp++->setDouble(d)
 #define PUSH_INT32(i)            REGS.sp++->setInt32(i)
+#define PUSH_SYMBOL(s)           REGS.sp++->setSymbol(s)
 #define PUSH_STRING(s)           do { REGS.sp++->setString(s); assertSameCompartmentDebugOnly(cx, REGS.sp[-1]); } while (0)
 #define PUSH_OBJECT(obj)         do { REGS.sp++->setObject(obj); assertSameCompartmentDebugOnly(cx, REGS.sp[-1]); } while (0)
 #define PUSH_OBJECT_OR_NULL(obj) do { REGS.sp++->setObjectOrNull(obj); assertSameCompartmentDebugOnly(cx, REGS.sp[-1]); } while (0)
@@ -1611,7 +1612,6 @@ CASE(EnableInterruptsPseudoOpcode)
 /* Various 1-byte no-ops. */
 CASE(JSOP_NOP)
 CASE(JSOP_UNUSED2)
-CASE(JSOP_UNUSED45)
 CASE(JSOP_UNUSED46)
 CASE(JSOP_UNUSED47)
 CASE(JSOP_UNUSED48)
@@ -2755,6 +2755,10 @@ CASE(JSOP_TOSTRING)
 }
 END_CASE(JSOP_TOSTRING)
 
+CASE(JSOP_SYMBOL)
+    PUSH_SYMBOL(cx->wellKnownSymbols().get(GET_UINT8(REGS.pc)));
+END_CASE(JSOP_SYMBOL)
+
 CASE(JSOP_OBJECT)
 {
     RootedObject &ref = rootObject0;
diff --git a/js/src/vm/Opcodes.h b/js/src/vm/Opcodes.h
index f0de8c52fc72..6984a4c6468e 100644
--- a/js/src/vm/Opcodes.h
+++ b/js/src/vm/Opcodes.h
@@ -416,7 +416,15 @@
      */ \
     macro(JSOP_DUPAT,     44, "dupat",      NULL,         4,  0,  1,  JOF_UINT24) \
     \
-    macro(JSOP_UNUSED45,  45, "unused45",   NULL,         1,  0,  0,  JOF_BYTE) \
+    /*
+     * Push a well-known symbol onto the operand stack.
+     *   Category: Literals
+     *   Type: Constants
+     *   Operands: uint8_t n, the JS::SymbolCode of the symbol to use
+     *   Stack: => symbol
+     */ \
+    macro(JSOP_SYMBOL,    45, "symbol",     NULL,         2,  0,  1,  JOF_UINT8) \
+    \
     macro(JSOP_UNUSED46,  46, "unused46",   NULL,         1,  0,  0,  JOF_BYTE) \
     macro(JSOP_UNUSED47,  47, "unused47",   NULL,         1,  0,  0,  JOF_BYTE) \
     macro(JSOP_UNUSED48,  48, "unused48",   NULL,         1,  0,  0,  JOF_BYTE) \
diff --git a/js/src/vm/PIC.cpp b/js/src/vm/PIC.cpp
index 455b7c40311e..46fbf946d736 100644
--- a/js/src/vm/PIC.cpp
+++ b/js/src/vm/PIC.cpp
@@ -44,8 +44,9 @@ js::ForOfPIC::Chain::initialize(JSContext *cx)
     // do set disabled_ now, and clear it later when we succeed.
     disabled_ = true;
 
-    // Look up '@@iterator' on Array.prototype, ensure it's a slotful shape.
-    Shape *iterShape = arrayProto->nativeLookup(cx, cx->names().std_iterator);
+    // Look up Array.prototype[@@iterator], ensure it's a slotful shape.
+    Shape *iterShape =
+        arrayProto->nativeLookup(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().iterator));
     if (!iterShape || !iterShape->hasSlot() || !iterShape->hasDefaultGetter())
         return true;
 
@@ -144,8 +145,8 @@ js::ForOfPIC::Chain::tryOptimizeArray(JSContext *cx, HandleObject array, bool *o
     if (!isOptimizableArray(array))
         return true;
 
-    // Ensure array doesn't define '@@iterator' directly.
-    if (array->nativeLookup(cx, cx->names().std_iterator))
+    // Ensure array doesn't define @@iterator directly.
+    if (array->nativeLookup(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().iterator)))
         return true;
 
     // Good to optimize now, create stub to add.
@@ -198,7 +199,7 @@ js::ForOfPIC::Chain::isArrayStateStillSane()
     if (arrayProto_->lastProperty() != arrayProtoShape_)
         return false;
 
-    // Ensure that Array.prototype['@@iterator'] contains the
+    // Ensure that Array.prototype[@@iterator] contains the
     // canonical iterator function.
     if (arrayProto_->getSlot(arrayProtoIteratorSlot_) != canonicalIteratorFunc_)
         return false;
diff --git a/js/src/vm/PIC.h b/js/src/vm/PIC.h
index 8aa04f7706b2..ff76bfd95309 100644
--- a/js/src/vm/PIC.h
+++ b/js/src/vm/PIC.h
@@ -130,7 +130,7 @@ struct ForOfPIC
 
     /*
      * A ForOfPIC has only one kind of stub for now: one that holds the shape
-     * of an array object that does not override its '@@iterator' property.
+     * of an array object that does not override its @@iterator property.
      */
     class Stub : public BaseStub
     {
@@ -164,8 +164,8 @@ struct ForOfPIC
      *  ArrayIterator.prototype's shape (arrayIteratorProtoShape_)
      *      To ensure that an ArrayIterator.prototype has not been modified.
      *
-     *  Array.prototype's slot number for '@@iterator' (arrayProtoIteratorSlot_)
-     *  Array.prototype's canonical value for '@@iterator' (canonicalIteratorFunc_)
+     *  Array.prototype's slot number for @@iterator (arrayProtoIteratorSlot_)
+     *  Array.prototype's canonical value for @@iterator (canonicalIteratorFunc_)
      *      To quickly retreive and ensure that the iterator constructor
      *      stored in the slot has not changed.
      *
@@ -182,7 +182,7 @@ struct ForOfPIC
         HeapPtrObject arrayIteratorProto_;
 
         // Shape of matching Array.prototype object, and slot containing
-        // the '@@iterator' for it, and the canonical value.
+        // the @@iterator for it, and the canonical value.
         HeapPtrShape arrayProtoShape_;
         uint32_t arrayProtoIteratorSlot_;
         HeapValue canonicalIteratorFunc_;
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index 5544a6ab816e..525f6673db50 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -1256,6 +1256,12 @@ CloneValue(JSContext *cx, HandleValue selfHostedValue, MutableHandleValue vp)
         if (!clone)
             return false;
         vp.setString(clone);
+    } else if (selfHostedValue.isSymbol()) {
+        // Well-known symbols are shared.
+        JS::Symbol *sym = selfHostedValue.toSymbol();
+        MOZ_ASSERT(sym->isWellKnownSymbol());
+        MOZ_ASSERT(cx->wellKnownSymbols().get(size_t(sym->code())) == sym);
+        vp.set(selfHostedValue);
     } else {
         MOZ_CRASH("Self-hosting CloneValue can't clone given value.");
     }
diff --git a/js/src/vm/TypedArrayObject.cpp b/js/src/vm/TypedArrayObject.cpp
index cb4535fcc84c..fdf2c2160b17 100644
--- a/js/src/vm/TypedArrayObject.cpp
+++ b/js/src/vm/TypedArrayObject.cpp
@@ -1590,7 +1590,7 @@ TypedArrayObject::setElement(TypedArrayObject &obj, uint32_t index, double d)
 
 #define IMPL_TYPED_ARRAY_STATICS(_typedArray)                                      \
 const JSFunctionSpec _typedArray##Object::jsfuncs[] = {                            \
-    JS_SELF_HOSTED_FN("@@iterator", "ArrayValues", 0, 0),                          \
+    JS_SELF_HOSTED_SYM_FN(iterator, "ArrayValues", 0, 0),                          \
     JS_FN("subarray", _typedArray##Object::fun_subarray, 2, JSFUN_GENERIC_NATIVE), \
     JS_FN("set", _typedArray##Object::fun_set, 2, JSFUN_GENERIC_NATIVE),           \
     JS_FN("copyWithin", _typedArray##Object::fun_copyWithin, 2, JSFUN_GENERIC_NATIVE), \
diff --git a/js/xpconnect/tests/chrome/test_xrayToJS.xul b/js/xpconnect/tests/chrome/test_xrayToJS.xul
index d5fdff2aa673..8b13c77ed3c6 100644
--- a/js/xpconnect/tests/chrome/test_xrayToJS.xul
+++ b/js/xpconnect/tests/chrome/test_xrayToJS.xul
@@ -174,14 +174,14 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=933681
     ["length", "toSource", "toString", "toLocaleString", "join", "reverse", "sort", "push",
       "pop", "shift", "unshift", "splice", "concat", "slice", "lastIndexOf", "indexOf",
       "forEach", "map", "reduce", "reduceRight", "filter", "some", "every", "find",
-      "findIndex", "copyWithin", "fill", "@@iterator", "entries", "keys", "constructor"];
+      "findIndex", "copyWithin", "fill", Symbol.iterator, "entries", "keys", "constructor"];
   if (isNightlyBuild) {
     let pjsMethods = ['mapPar', 'reducePar', 'scanPar', 'scatterPar', 'filterPar'];
     gPrototypeProperties['Array'] = gPrototypeProperties['Array'].concat(pjsMethods);
   }
   for (var c of typedArrayClasses) {
     gPrototypeProperties[c] = ["constructor", "BYTES_PER_ELEMENT", "length", "buffer",
-                               "byteLength", "byteOffset", "@@iterator", "subarray", "set",
+                               "byteLength", "byteOffset", "Symbol.iterator", "subarray", "set",
                                "copyWithin"];
   }
   for (var c of errorObjectClasses) {
@@ -211,9 +211,13 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=933681
     let xrayProto = Object.getPrototypeOf(xray);
     let localProto = window[classname].prototype;
     is(Object.getOwnPropertyNames(localProto).sort().toSource(),
-       gPrototypeProperties[classname].sort().toSource(),
+       gPrototypeProperties[classname].filter(id => typeof id === "string").sort().toSource(),
        "A property on the " + classname +
-       " prototype has changed! You need a security audit from an XPConnect peer");
+       " prototype has been changed! You need a security audit from an XPConnect peer");
+    is(Object.getOwnPropertySymbols(localProto).map(uneval).sort().toSource(),
+       gPrototypeProperties[classname].filter(id => typeof id !== "string").map(uneval).sort().toSource(),
+       "A symbol-keyed property on the " + classname +
+       " prototype has been changed! You need a security audit from an XPConnect peer");
 
     let protoProps = filterOut(Object.getOwnPropertyNames(localProto), propsToSkip).sort();
     let protoCallables = protoProps.filter(name => Object.getOwnPropertyDescriptor(localProto, name).get ||
diff --git a/toolkit/modules/Promise-backend.js b/toolkit/modules/Promise-backend.js
index 2390b01e650b..852df9c47b87 100644
--- a/toolkit/modules/Promise-backend.js
+++ b/toolkit/modules/Promise-backend.js
@@ -511,7 +511,7 @@ Promise.reject = function (aReason)
  */
 Promise.all = function (aValues)
 {
-  if (aValues == null || typeof(aValues["@@iterator"]) != "function") {
+  if (aValues == null || typeof(aValues[Symbol.iterator]) != "function") {
     throw new Error("Promise.all() expects an iterable.");
   }
 
@@ -562,7 +562,7 @@ Promise.all = function (aValues)
  */
 Promise.race = function (aValues)
 {
-  if (aValues == null || typeof(aValues["@@iterator"]) != "function") {
+  if (aValues == null || typeof(aValues[Symbol.iterator]) != "function") {
     throw new Error("Promise.race() expects an iterable.");
   }