diff --git a/browser/devtools/debugger/VariablesView.jsm b/browser/devtools/debugger/VariablesView.jsm
index cc50de2eb35e..d1521ee0404d 100644
--- a/browser/devtools/debugger/VariablesView.jsm
+++ b/browser/devtools/debugger/VariablesView.jsm
@@ -61,7 +61,7 @@ VariablesView.prototype = {
    */
   empty: function VV_empty(aTimeout = LAZY_EMPTY_DELAY) {
     // If there are no items in this container, emptying is useless.
-    if (!this._store.size()) {
+    if (!this._store.size) {
       return;
     }
     // Check if this empty operation may be executed lazily.
@@ -110,7 +110,7 @@ VariablesView.prototype = {
       this._parent.removeChild(prevList);
       this._parent.appendChild(currList);
 
-      if (!this._store.size()) {
+      if (!this._store.size) {
         this._appendEmptyNotice();
       }
     }.bind(this), aTimeout);
diff --git a/browser/devtools/debugger/debugger-panes.js b/browser/devtools/debugger/debugger-panes.js
index ddb6e260b075..9373da055882 100644
--- a/browser/devtools/debugger/debugger-panes.js
+++ b/browser/devtools/debugger/debugger-panes.js
@@ -812,7 +812,7 @@ create({ constructor: GlobalSearchView, proto: MenuContainer.prototype }, {
    */
   _fetchSources: function DVGS__fetchSources(aFetchCallback, aFetchedCallback, aLocations) {
     // If all the sources were already fetched, then don't do anything.
-    if (this._cache.size() == aLocations.length) {
+    if (this._cache.size == aLocations.length) {
       aFetchedCallback();
       return;
     }
@@ -840,7 +840,7 @@ create({ constructor: GlobalSearchView, proto: MenuContainer.prototype }, {
     this._cache.set(aLocation, aContents);
 
     // Check if all sources were fetched and stored in the cache.
-    if (this._cache.size() == this._sourcesCount) {
+    if (this._cache.size == this._sourcesCount) {
       this._onFetchSourcesFinished();
     }
   },
@@ -1151,7 +1151,7 @@ GlobalResults.prototype = {
   /**
    * Gets the number of source results in this store.
    */
-  get itemCount() this._store.size(),
+  get itemCount() this._store.size,
 
   _store: null
 };
diff --git a/browser/devtools/debugger/test/browser_dbg_scripts-searching-05.js b/browser/devtools/debugger/test/browser_dbg_scripts-searching-05.js
index 4aeda04f3f1d..6119a8ccdaaa 100644
--- a/browser/devtools/debugger/test/browser_dbg_scripts-searching-05.js
+++ b/browser/devtools/debugger/test/browser_dbg_scripts-searching-05.js
@@ -134,7 +134,7 @@ function testLocationChange()
   window.addEventListener("Debugger:GlobalSearch:CacheCleared", function _onCacheCleared(aEvent) {
     window.removeEventListener(aEvent.type, _onCacheCleared);
 
-    is(gSearchView._cache.size(), 0,
+    is(gSearchView._cache.size, 0,
       "The scripts sources cache for global searching should be cleared after a page navigation.")
 
     cacheCleared = true;
diff --git a/js/src/builtin/MapObject.cpp b/js/src/builtin/MapObject.cpp
index f29e78f88a8b..967c94ba4826 100644
--- a/js/src/builtin/MapObject.cpp
+++ b/js/src/builtin/MapObject.cpp
@@ -947,8 +947,12 @@ Class MapObject::class_ = {
     mark
 };
 
+JSPropertySpec MapObject::properties[] = {
+    JS_PSG("size", size, 0),
+    JS_PS_END
+};
+
 JSFunctionSpec MapObject::methods[] = {
-    JS_FN("size", size, 0, 0),
     JS_FN("get", get, 1, 0),
     JS_FN("has", has, 1, 0),
     JS_FN("set", set, 2, 0),
@@ -960,7 +964,7 @@ JSFunctionSpec MapObject::methods[] = {
 
 static JSObject *
 InitClass(JSContext *cx, Handle<GlobalObject*> global, Class *clasp, JSProtoKey key, Native construct,
-          JSFunctionSpec *methods)
+          JSPropertySpec *properties, JSFunctionSpec *methods)
 {
     Rooted<JSObject*> proto(cx, global->createBlankPrototype(cx, clasp));
     if (!proto)
@@ -970,7 +974,7 @@ InitClass(JSContext *cx, Handle<GlobalObject*> global, Class *clasp, JSProtoKey
     Rooted<JSFunction*> ctor(cx, global->createConstructor(cx, construct, ClassName(key, cx), 1));
     if (!ctor ||
         !LinkConstructorAndPrototype(cx, ctor, proto) ||
-        !DefinePropertiesAndBrand(cx, proto, NULL, methods) ||
+        !DefinePropertiesAndBrand(cx, proto, properties, methods) ||
         !DefineConstructorAndPrototype(cx, global, key, ctor, proto))
     {
         return NULL;
@@ -982,7 +986,7 @@ JSObject *
 MapObject::initClass(JSContext *cx, JSObject *obj)
 {
     Rooted<GlobalObject*> global(cx, &obj->asGlobal());
-    return InitClass(cx, global, &class_, JSProto_Map, construct, methods);
+    return InitClass(cx, global, &class_, JSProto_Map, construct, properties, methods);
 }
 
 template <class Range>
@@ -1410,8 +1414,12 @@ Class SetObject::class_ = {
     mark
 };
 
+JSPropertySpec SetObject::properties[] = {
+    JS_PSG("size", size, 0),
+    JS_PS_END
+};
+
 JSFunctionSpec SetObject::methods[] = {
-    JS_FN("size", size, 0, 0),
     JS_FN("has", has, 1, 0),
     JS_FN("add", add, 1, 0),
     JS_FN("delete", delete_, 1, 0),
@@ -1424,7 +1432,7 @@ JSObject *
 SetObject::initClass(JSContext *cx, JSObject *obj)
 {
     Rooted<GlobalObject*> global(cx, &obj->asGlobal());
-    return InitClass(cx, global, &class_, JSProto_Set, construct, methods);
+    return InitClass(cx, global, &class_, JSProto_Set, construct, properties, methods);
 }
 
 void
diff --git a/js/src/builtin/MapObject.h b/js/src/builtin/MapObject.h
index 96d440e4c2d8..32bc9482e827 100644
--- a/js/src/builtin/MapObject.h
+++ b/js/src/builtin/MapObject.h
@@ -84,6 +84,7 @@ class MapObject : public JSObject {
     static JSObject *initClass(JSContext *cx, JSObject *obj);
     static Class class_;
   private:
+    static JSPropertySpec properties[];
     static JSFunctionSpec methods[];
     ValueMap *getData() { return static_cast<ValueMap *>(getPrivate()); }
     static ValueMap & extract(CallReceiver call);
@@ -114,6 +115,7 @@ class SetObject : public JSObject {
     static JSObject *initClass(JSContext *cx, JSObject *obj);
     static Class class_;
   private:
+    static JSPropertySpec properties[];
     static JSFunctionSpec methods[];
     ValueSet *getData() { return static_cast<ValueSet *>(getPrivate()); }
     static ValueSet & extract(CallReceiver call);
diff --git a/js/src/jit-test/tests/collections/Map-clear-1.js b/js/src/jit-test/tests/collections/Map-clear-1.js
index e427a42a3dad..0684c400eea8 100644
--- a/js/src/jit-test/tests/collections/Map-clear-1.js
+++ b/js/src/jit-test/tests/collections/Map-clear-1.js
@@ -3,6 +3,6 @@
 var m = Map();
 for (var i = 0; i < 2; i++) {
     m.clear();
-    assertEq(m.size(), 0);
+    assertEq(m.size, 0);
     assertEq(m.has(undefined), false);
 }
diff --git a/js/src/jit-test/tests/collections/Map-clear-2.js b/js/src/jit-test/tests/collections/Map-clear-2.js
index c9eea1debbcf..27fa4cd5ea89 100644
--- a/js/src/jit-test/tests/collections/Map-clear-2.js
+++ b/js/src/jit-test/tests/collections/Map-clear-2.js
@@ -1,9 +1,9 @@
 // Clearing a Map removes its entries; the Map remains usable afterwards.
 
 var m = Map([["a", "b"], ["b", "c"]]);
-assertEq(m.size(), 2);
+assertEq(m.size, 2);
 m.clear();
-assertEq(m.size(), 0);
+assertEq(m.size, 0);
 assertEq(m.has("a"), false);
 assertEq(m.get("a"), undefined);
 assertEq(m.delete("a"), false);
@@ -12,6 +12,6 @@ for (var pair of m)
     throw "FAIL";  // shouldn't be any pairs
 
 m.set("c", "d");
-assertEq(m.size(), 1);
+assertEq(m.size, 1);
 assertEq(m.has("a"), false);
 assertEq(m.has("b"), false);
diff --git a/js/src/jit-test/tests/collections/Map-clear-3.js b/js/src/jit-test/tests/collections/Map-clear-3.js
index 28c76d9ff10d..6666479d930e 100644
--- a/js/src/jit-test/tests/collections/Map-clear-3.js
+++ b/js/src/jit-test/tests/collections/Map-clear-3.js
@@ -3,8 +3,8 @@
 var m = Map();
 for (var i = 0; i < 100; i++)
     m.set(i, i);
-assertEq(m.size(), i);
+assertEq(m.size, i);
 m.clear();
-assertEq(m.size(), 0);
+assertEq(m.size, 0);
 m.set("a", 1);
 assertEq(m.get("a"), 1);
diff --git a/js/src/jit-test/tests/collections/Map-clear-4.js b/js/src/jit-test/tests/collections/Map-clear-4.js
index 1edddf9a9bda..6e9fc12da0d5 100644
--- a/js/src/jit-test/tests/collections/Map-clear-4.js
+++ b/js/src/jit-test/tests/collections/Map-clear-4.js
@@ -5,6 +5,6 @@ for (var [k, v] of m)
     if (k !== "c")
         m.delete(k);
 m.clear();
-assertEq(m.size(), 0);
+assertEq(m.size, 0);
 assertEq(m.has("c"), false);
 assertEq(m.has("d"), false);
diff --git a/js/src/jit-test/tests/collections/Map-clear-5.js b/js/src/jit-test/tests/collections/Map-clear-5.js
index f699d126ab99..264365e48076 100644
--- a/js/src/jit-test/tests/collections/Map-clear-5.js
+++ b/js/src/jit-test/tests/collections/Map-clear-5.js
@@ -6,9 +6,9 @@ var m1 = Map(data), m2 = Map(data);
 delete Map.prototype.delete;
 delete Map.prototype.iterator;
 m1.clear();
-assertEq(m1.size(), 0);
+assertEq(m1.size, 0);
 
 Map.prototype.delete = function () { throw "FAIL"; };
 Map.prototype.iterator = function () { throw "FAIL"; };
 m2.clear();
-assertEq(m2.size(), 0);
+assertEq(m2.size, 0);
diff --git a/js/src/jit-test/tests/collections/Map-constructor-1.js b/js/src/jit-test/tests/collections/Map-constructor-1.js
index 304747ff8aec..c3033f15c356 100644
--- a/js/src/jit-test/tests/collections/Map-constructor-1.js
+++ b/js/src/jit-test/tests/collections/Map-constructor-1.js
@@ -1,6 +1,6 @@
 // The Map constructor creates an empty Map by default.
 
-assertEq(Map().size(), 0);
-assertEq((new Map).size(), 0);
-assertEq(Map(undefined).size(), 0);
-assertEq(new Map(undefined).size(), 0);
+assertEq(Map().size, 0);
+assertEq((new Map).size, 0);
+assertEq(Map(undefined).size, 0);
+assertEq(new Map(undefined).size, 0);
diff --git a/js/src/jit-test/tests/collections/Map-constructor-3.js b/js/src/jit-test/tests/collections/Map-constructor-3.js
index 76881a51dfd4..bb388b3a33a8 100644
--- a/js/src/jit-test/tests/collections/Map-constructor-3.js
+++ b/js/src/jit-test/tests/collections/Map-constructor-3.js
@@ -2,7 +2,7 @@
 
 var arr = [["a"], ["b"], ["c"]];
 var m = Map(arr);
-assertEq(m.size(), 3);
+assertEq(m.size, 3);
 for (var [k, _] of arr) {
     assertEq(m.has(k), true);
     assertEq(m.get(k), undefined);
diff --git a/js/src/jit-test/tests/collections/Map-constructor-duplicates.js b/js/src/jit-test/tests/collections/Map-constructor-duplicates.js
index 9fade316ac37..3be687471219 100644
--- a/js/src/jit-test/tests/collections/Map-constructor-duplicates.js
+++ b/js/src/jit-test/tests/collections/Map-constructor-duplicates.js
@@ -5,4 +5,4 @@ var m = Map(arg);
 assertEq(m.get("zero"), 0);
 assertEq(m.get("one"), 1);
 assertEq(m.get("two"), 2);
-assertEq(m.size(), 3);
+assertEq(m.size, 3);
diff --git a/js/src/jit-test/tests/collections/Map-constructor-generator-1.js b/js/src/jit-test/tests/collections/Map-constructor-generator-1.js
index 21fc6c5e70b3..3278f6704dde 100644
--- a/js/src/jit-test/tests/collections/Map-constructor-generator-1.js
+++ b/js/src/jit-test/tests/collections/Map-constructor-generator-1.js
@@ -12,7 +12,7 @@ function data(n) {
 
 var m = Map(data(50));
 assertEq(done, true);  // the constructor consumes the argument
-assertEq(m.size(), 50);
+assertEq(m.size, 50);
 assertEq(m.get(""), 0);
 assertEq(m.get("....."), 5);
 assertEq(m.get(Array(49+1).join(".")), 49);
diff --git a/js/src/jit-test/tests/collections/Map-constructor-generator-2.js b/js/src/jit-test/tests/collections/Map-constructor-generator-2.js
index afbe2e1d38c7..d2bf399ba7b9 100644
--- a/js/src/jit-test/tests/collections/Map-constructor-generator-2.js
+++ b/js/src/jit-test/tests/collections/Map-constructor-generator-2.js
@@ -2,7 +2,7 @@
 
 var arr = [1, 2, "green", "red"];
 var m = Map([v, v] for (v of arr));
-assertEq(m.size(), 4);
+assertEq(m.size, 4);
 
 for (var i = 0; i < 4; i++)
     assertEq(m.get(arr[i]), arr[i]);
diff --git a/js/src/jit-test/tests/collections/Map-constructor-generator-3.js b/js/src/jit-test/tests/collections/Map-constructor-generator-3.js
index 44e9479f83bb..cddcbb5d43cc 100644
--- a/js/src/jit-test/tests/collections/Map-constructor-generator-3.js
+++ b/js/src/jit-test/tests/collections/Map-constructor-generator-3.js
@@ -1,8 +1,8 @@
 // The argument to Map may be a generator-iterator that produces no values.
 
-assertEq(Map(x for (x of [])).size(), 0);
+assertEq(Map(x for (x of [])).size, 0);
 
 function none() {
     if (0) yield 0;
 }
-assertEq(Map(none()).size(), 0);
+assertEq(Map(none()).size, 0);
diff --git a/js/src/jit-test/tests/collections/Map-delete-size.js b/js/src/jit-test/tests/collections/Map-delete-size.js
index 5ece89c63a61..44189f89ea1c 100644
--- a/js/src/jit-test/tests/collections/Map-delete-size.js
+++ b/js/src/jit-test/tests/collections/Map-delete-size.js
@@ -2,13 +2,13 @@
 
 var m = Map();
 m.delete(3);
-assertEq(m.size(), 0);
+assertEq(m.size, 0);
 m.set({}, 'ok');
 m.set(Math, 'ok');
-assertEq(m.size(), 2);
+assertEq(m.size, 2);
 m.delete({});
-assertEq(m.size(), 2);
+assertEq(m.size, 2);
 m.delete(Math);
-assertEq(m.size(), 1);
+assertEq(m.size, 1);
 m.delete(Math);
-assertEq(m.size(), 1);
+assertEq(m.size, 1);
diff --git a/js/src/jit-test/tests/collections/Map-iterator-add-1.js b/js/src/jit-test/tests/collections/Map-iterator-add-1.js
index 13c2c82ce969..01d20822c9cb 100644
--- a/js/src/jit-test/tests/collections/Map-iterator-add-1.js
+++ b/js/src/jit-test/tests/collections/Map-iterator-add-1.js
@@ -12,4 +12,4 @@ for (let [k, v] of map) {
     force(v);
 }
 assertEq(log, '5;4;3;2;1;0;');
-assertEq(map.size(), 6);
+assertEq(map.size, 6);
diff --git a/js/src/jit-test/tests/collections/Map-iterator-order.js b/js/src/jit-test/tests/collections/Map-iterator-order.js
index 388361e4192f..72161886c591 100644
--- a/js/src/jit-test/tests/collections/Map-iterator-order.js
+++ b/js/src/jit-test/tests/collections/Map-iterator-order.js
@@ -5,7 +5,7 @@ load(libdir + "eqArrayHelper.js");
 var map = Map();
 for (var i = 7; i !== 1; i = i * 7 % 1117)
     map.set("" + i, i);
-assertEq(map.size(), 557);
+assertEq(map.size, 557);
 
 i = 7;
 for (var pair of map) {
diff --git a/js/src/jit-test/tests/collections/Map-iterator-pairs-3.js b/js/src/jit-test/tests/collections/Map-iterator-pairs-3.js
index 54a8e38a851b..944eded65596 100644
--- a/js/src/jit-test/tests/collections/Map-iterator-pairs-3.js
+++ b/js/src/jit-test/tests/collections/Map-iterator-pairs-3.js
@@ -9,4 +9,4 @@ assertEq(pair[0], 'b');
 assertEq(pair[1], 2);
 assertEq(map.get('a'), 1);
 assertEq(map.has('b'), false);
-assertEq(map.size(), 1);
+assertEq(map.size, 1);
diff --git a/js/src/jit-test/tests/collections/Map-iterator-remove-5.js b/js/src/jit-test/tests/collections/Map-iterator-remove-5.js
index 7e255fde25cc..c7e7d9ff096d 100644
--- a/js/src/jit-test/tests/collections/Map-iterator-remove-5.js
+++ b/js/src/jit-test/tests/collections/Map-iterator-remove-5.js
@@ -18,5 +18,5 @@ for (var [k, v] of map) {
     }
 }
 assertEq(log, 'ABCDEFGHIJKLMNOPQRST');
-assertEq(map.size(), 1);  // Only the last entry remains.
+assertEq(map.size, 1);  // Only the last entry remains.
 assertEq(map.get('T'), 19);
diff --git a/js/src/jit-test/tests/collections/Map-iterator-remove-6.js b/js/src/jit-test/tests/collections/Map-iterator-remove-6.js
index 3be1b4569f76..e25199482c7c 100644
--- a/js/src/jit-test/tests/collections/Map-iterator-remove-6.js
+++ b/js/src/jit-test/tests/collections/Map-iterator-remove-6.js
@@ -11,7 +11,7 @@ var iter = map.iterator();
 assertEq(iter.next()[0], 0);
 for (var i = 0; i < 30; i++)
     map.delete(i);
-assertEq(map.size(), 2);
+assertEq(map.size, 2);
 for (var i = 32; i < 100; i++)
     map.set(i, i);  // eventually triggers compaction
 
diff --git a/js/src/jit-test/tests/collections/Map-set-size.js b/js/src/jit-test/tests/collections/Map-set-size.js
index f0a4cdfde148..10f967087cd2 100644
--- a/js/src/jit-test/tests/collections/Map-set-size.js
+++ b/js/src/jit-test/tests/collections/Map-set-size.js
@@ -2,13 +2,13 @@
 
 var m = Map();
 m.set('a', 0);
-assertEq(m.size(), 1);
+assertEq(m.size, 1);
 m.set('a', 0);
-assertEq(m.size(), 1);
+assertEq(m.size, 1);
 m.set('a', undefined);
-assertEq(m.size(), 1);
+assertEq(m.size, 1);
 
 m.set('b', 2);
-assertEq(m.size(), 2);
+assertEq(m.size, 2);
 m.set('a', 1);
-assertEq(m.size(), 2);
+assertEq(m.size, 2);
diff --git a/js/src/jit-test/tests/collections/Map-size.js b/js/src/jit-test/tests/collections/Map-size.js
index 325abdc1a9ab..ef5d786479a3 100644
--- a/js/src/jit-test/tests/collections/Map-size.js
+++ b/js/src/jit-test/tests/collections/Map-size.js
@@ -2,5 +2,5 @@
 
 var m1 = Map(), m2 = Map();
 m1.set("x", 3);
-assertEq(m1.size(), 1);
-assertEq(m2.size(), 0);
+assertEq(m1.size, 1);
+assertEq(m2.size, 0);
diff --git a/js/src/jit-test/tests/collections/Map-surfaces-1.js b/js/src/jit-test/tests/collections/Map-surfaces-1.js
index abfc950955ca..2b620aeeb33c 100644
--- a/js/src/jit-test/tests/collections/Map-surfaces-1.js
+++ b/js/src/jit-test/tests/collections/Map-surfaces-1.js
@@ -27,9 +27,15 @@ function checkMethod(name, arity) {
     assertEq(desc.value.length, arity);
 }
 
-checkMethod("size", 0);
 checkMethod("get", 1);
 checkMethod("has", 1);
 checkMethod("set", 2);
 checkMethod("delete", 1);
+
+var desc = Object.getOwnPropertyDescriptor(Map.prototype, "size");
+assertEq(desc.enumerable, false);
+assertEq(desc.configurable, true);
+assertEq(typeof desc.get, 'function');
+assertEq(desc.get.length, 0);
+assertEq(desc.set, undefined);
 checkMethod("clear", 0);
diff --git a/js/src/jit-test/tests/collections/Map-surfaces-2.js b/js/src/jit-test/tests/collections/Map-surfaces-2.js
index 2478e3671091..78d27ac761df 100644
--- a/js/src/jit-test/tests/collections/Map-surfaces-2.js
+++ b/js/src/jit-test/tests/collections/Map-surfaces-2.js
@@ -8,13 +8,15 @@ function testcase(obj, fn) {
     assertThrowsInstanceOf(function () { fn.apply(obj, args); }, TypeError);
 }
 
+var Map_size_getter = Object.getOwnPropertyDescriptor(Map.prototype, "size").get;
+
 function test(obj) {
-    testcase(obj, Map.prototype.size);
     testcase(obj, Map.prototype.get, "x");
     testcase(obj, Map.prototype.has, "x");
     testcase(obj, Map.prototype.set, "x", 1);
     testcase(obj, Map.prototype.delete, "x");
     testcase(obj, Map.prototype.clear);
+    testcase(obj, Map_size_getter);
 }
 
 test(Map.prototype);
diff --git a/js/src/jit-test/tests/collections/Set-add-size.js b/js/src/jit-test/tests/collections/Set-add-size.js
index 381bd111d13d..ceb4bdbff926 100644
--- a/js/src/jit-test/tests/collections/Set-add-size.js
+++ b/js/src/jit-test/tests/collections/Set-add-size.js
@@ -1,11 +1,11 @@
-// set.add(v) increments set.size() iff the set did not already contain v.
+// set.add(v) increments set.size iff the set did not already contain v.
 
 var s = Set();
 for (var i = 0; i < 10; i++) {
-    assertEq(s.size(), i);
+    assertEq(s.size, i);
     s.add(i);
 }
 for (var i = 0; i < 10; i++) {
-    assertEq(s.size(), 10);
+    assertEq(s.size, 10);
     s.add(i);
 }
diff --git a/js/src/jit-test/tests/collections/Set-clear-1.js b/js/src/jit-test/tests/collections/Set-clear-1.js
index 357f5706332b..c866769bcc6d 100644
--- a/js/src/jit-test/tests/collections/Set-clear-1.js
+++ b/js/src/jit-test/tests/collections/Set-clear-1.js
@@ -3,6 +3,6 @@
 var s = Set();
 for (var i = 0; i < 2; i++) {
     s.clear();
-    assertEq(s.size(), 0);
+    assertEq(s.size, 0);
     assertEq(s.has(undefined), false);
 }
diff --git a/js/src/jit-test/tests/collections/Set-clear-2.js b/js/src/jit-test/tests/collections/Set-clear-2.js
index 2e5b6add0953..b711daa978e3 100644
--- a/js/src/jit-test/tests/collections/Set-clear-2.js
+++ b/js/src/jit-test/tests/collections/Set-clear-2.js
@@ -1,9 +1,9 @@
 // Clearing a Set removes its elements; the Set remains usable afterwards.
 
 var s = Set(["x", "y", "z", "z", "y"]);
-assertEq(s.size(), 3);
+assertEq(s.size, 3);
 s.clear();
-assertEq(s.size(), 0);
+assertEq(s.size, 0);
 assertEq(s.has("x"), false);
 assertEq(s.delete("x"), false);
 assertEq(s.has("z"), false);
@@ -11,6 +11,6 @@ for (var v of s)
     throw "FAIL";  // shouldn't be any elements
 
 s.add("y");
-assertEq(s.size(), 1);
+assertEq(s.size, 1);
 assertEq(s.has("x"), false);
 assertEq(s.has("z"), false);
diff --git a/js/src/jit-test/tests/collections/Set-clear-3.js b/js/src/jit-test/tests/collections/Set-clear-3.js
index 9b28e2ffe783..6c08b99cdc70 100644
--- a/js/src/jit-test/tests/collections/Set-clear-3.js
+++ b/js/src/jit-test/tests/collections/Set-clear-3.js
@@ -3,8 +3,8 @@
 var s = Set();
 for (var i = 0; i < 100; i++)
     s.add(i);
-assertEq(s.size(), i);
+assertEq(s.size, i);
 s.clear();
-assertEq(s.size(), 0);
+assertEq(s.size, 0);
 s.add(12);
 assertEq(s.has(12), true);
diff --git a/js/src/jit-test/tests/collections/Set-clear-4.js b/js/src/jit-test/tests/collections/Set-clear-4.js
index 01bfb5805132..8f6eb4aeda9a 100644
--- a/js/src/jit-test/tests/collections/Set-clear-4.js
+++ b/js/src/jit-test/tests/collections/Set-clear-4.js
@@ -5,6 +5,6 @@ for (var v of s)
     if (v !== "c")
         s.delete(v);
 s.clear();
-assertEq(s.size(), 0);
+assertEq(s.size, 0);
 assertEq(s.has("c"), false);
 assertEq(s.has("d"), false);
diff --git a/js/src/jit-test/tests/collections/Set-clear-5.js b/js/src/jit-test/tests/collections/Set-clear-5.js
index fef8a2897ed4..813b0d0fd707 100644
--- a/js/src/jit-test/tests/collections/Set-clear-5.js
+++ b/js/src/jit-test/tests/collections/Set-clear-5.js
@@ -6,9 +6,9 @@ var s1 = Set(data), s2 = Set(data);
 delete Set.prototype.delete;
 delete Set.prototype.iterator;
 s1.clear();
-assertEq(s1.size(), 0);
+assertEq(s1.size, 0);
 
 Set.prototype.delete = function () { throw "FAIL"; };
 Set.prototype.iterator = function () { throw "FAIL"; };
 s2.clear();
-assertEq(s2.size(), 0);
+assertEq(s2.size, 0);
diff --git a/js/src/jit-test/tests/collections/Set-constructor-1.js b/js/src/jit-test/tests/collections/Set-constructor-1.js
index f7c75067ee73..2466468d6dad 100644
--- a/js/src/jit-test/tests/collections/Set-constructor-1.js
+++ b/js/src/jit-test/tests/collections/Set-constructor-1.js
@@ -1,6 +1,6 @@
 // The Set constructor creates an empty Set by default.
 
-assertEq(Set().size(), 0);
-assertEq((new Set).size(), 0);
-assertEq(Set(undefined).size(), 0);
-assertEq(new Set(undefined).size(), 0);
+assertEq(Set().size, 0);
+assertEq((new Set).size, 0);
+assertEq(Set(undefined).size, 0);
+assertEq(new Set(undefined).size, 0);
diff --git a/js/src/jit-test/tests/collections/Set-constructor-2.js b/js/src/jit-test/tests/collections/Set-constructor-2.js
index 92dccc84919e..0ec554fc9804 100644
--- a/js/src/jit-test/tests/collections/Set-constructor-2.js
+++ b/js/src/jit-test/tests/collections/Set-constructor-2.js
@@ -1,17 +1,17 @@
 // The Set constructor can take an argument that is an array.
 
 var s = Set([]);
-assertEq(s.size(), 0);
+assertEq(s.size, 0);
 assertEq(s.has(undefined), false);
 
 s = Set(["one", "two", "three"]);
-assertEq(s.size(), 3);
+assertEq(s.size, 3);
 assertEq(s.has("one"), true);
 assertEq(s.has("eleventeen"), false);
 
 var a = [{}, {}, {}];
 s = Set(a);
-assertEq(s.size(), 3);
+assertEq(s.size, 3);
 for (let obj of a)
     assertEq(s.has(obj), true);
 assertEq(s.has({}), false);
diff --git a/js/src/jit-test/tests/collections/Set-constructor-3.js b/js/src/jit-test/tests/collections/Set-constructor-3.js
index 7238c0610c39..9851cec39664 100644
--- a/js/src/jit-test/tests/collections/Set-constructor-3.js
+++ b/js/src/jit-test/tests/collections/Set-constructor-3.js
@@ -1,11 +1,11 @@
 // The argument to Set may contain a value multiple times. Duplicates are discarded.
 
-assertEq(Set(["testing", "testing", 123]).size(), 2);
+assertEq(Set(["testing", "testing", 123]).size, 2);
 
 var values = [undefined, null, false, NaN, 0, -0, 6.022e23, -Infinity, "", "xyzzy", {}, Math.sin];
 for (let v of values) {
     var a = [v, {}, {}, {}, v, {}, v, v];
     var s = Set(a);
-    assertEq(s.size(), 5);
+    assertEq(s.size, 5);
     assertEq(s.has(v), true);
 }
diff --git a/js/src/jit-test/tests/collections/Set-constructor-generator-1.js b/js/src/jit-test/tests/collections/Set-constructor-generator-1.js
index 26db09ba41e3..3b2263dacbe0 100644
--- a/js/src/jit-test/tests/collections/Set-constructor-generator-1.js
+++ b/js/src/jit-test/tests/collections/Set-constructor-generator-1.js
@@ -6,7 +6,7 @@ function hexData(n) {
 }
 
 var s = Set(hexData(256));
-assertEq(s.size(), 256);
+assertEq(s.size, 256);
 assertEq(s.has("0"), true);
 assertEq(s.has(0), false);
 assertEq(s.has("ff"), true);
diff --git a/js/src/jit-test/tests/collections/Set-constructor-generator-2.js b/js/src/jit-test/tests/collections/Set-constructor-generator-2.js
index 4e65253fe066..6e12cf64962b 100644
--- a/js/src/jit-test/tests/collections/Set-constructor-generator-2.js
+++ b/js/src/jit-test/tests/collections/Set-constructor-generator-2.js
@@ -1,7 +1,7 @@
 // The argument to Set can be a generator-expression.
 
 var s = Set(k * k for (k of [1, 2, 3, 4]));
-assertEq(s.size(), 4);
+assertEq(s.size, 4);
 assertEq(s.has(1), true);
 assertEq(s.has(4), true);
 assertEq(s.has(9), true);
diff --git a/js/src/jit-test/tests/collections/Set-delete-size.js b/js/src/jit-test/tests/collections/Set-delete-size.js
index e02234a99bd2..fbd2a1cd608b 100644
--- a/js/src/jit-test/tests/collections/Set-delete-size.js
+++ b/js/src/jit-test/tests/collections/Set-delete-size.js
@@ -1,15 +1,15 @@
-// set.delete(v) decrements set.size() iff the set contained v.
+// set.delete(v) decrements set.size iff the set contained v.
 
 var s = Set();
 for (var i = 0; i < 10; i++)
     s.add(i);
 
 for (var i = 10; i > 0; i--) {
-    assertEq(s.size(), i);
+    assertEq(s.size, i);
     assertEq(s.delete(i), false);
-    assertEq(s.size(), i);
+    assertEq(s.size, i);
     assertEq(s.delete(i - 1), true);
-    assertEq(s.size(), i - 1);
+    assertEq(s.size, i - 1);
     assertEq(s.delete(i - 1), false);
-    assertEq(s.size(), i - 1);
+    assertEq(s.size, i - 1);
 }
diff --git a/js/src/jit-test/tests/collections/Set-iterator-3.js b/js/src/jit-test/tests/collections/Set-iterator-3.js
index 96b586cc2b2d..760eda187023 100644
--- a/js/src/jit-test/tests/collections/Set-iterator-3.js
+++ b/js/src/jit-test/tests/collections/Set-iterator-3.js
@@ -2,7 +2,7 @@
 
 var arr = [{}, {}, {}, [], /xyz/, new Date];
 var set = Set(arr);
-assertEq(set.size(), arr.length);
+assertEq(set.size, arr.length);
 
 var i = 0;
 for (var x of set)
diff --git a/js/src/jit-test/tests/collections/Set-iterator-add-1.js b/js/src/jit-test/tests/collections/Set-iterator-add-1.js
index 2608984b1738..2d1c92011677 100644
--- a/js/src/jit-test/tests/collections/Set-iterator-add-1.js
+++ b/js/src/jit-test/tests/collections/Set-iterator-add-1.js
@@ -8,4 +8,4 @@ for (let x of set) {
         set.add(x - 1);
 }
 assertEq(log, '5;4;3;2;1;0;');
-assertEq(set.size(), 6);
+assertEq(set.size, 6);
diff --git a/js/src/jit-test/tests/collections/Set-iterator-order.js b/js/src/jit-test/tests/collections/Set-iterator-order.js
index fc5f33bad4a7..bc89debc66ab 100644
--- a/js/src/jit-test/tests/collections/Set-iterator-order.js
+++ b/js/src/jit-test/tests/collections/Set-iterator-order.js
@@ -4,7 +4,7 @@ var set = Set();
 var i;
 for (i = 7; i !== 1; i = i * 7 % 1117)
     set.add(i);
-assertEq(set.size(), 557);
+assertEq(set.size, 557);
 
 i = 7;
 for (var v of set) {
diff --git a/js/src/jit-test/tests/collections/Set-iterator-remove-5.js b/js/src/jit-test/tests/collections/Set-iterator-remove-5.js
index b72c09d1a21d..a74c1145d2b8 100644
--- a/js/src/jit-test/tests/collections/Set-iterator-remove-5.js
+++ b/js/src/jit-test/tests/collections/Set-iterator-remove-5.js
@@ -18,5 +18,5 @@ for (var x of set) {
     }
 }
 assertEq(log, str);
-assertEq(set.size(), 1);  // Elements 0 to 24 are removed, leaving only 25 (Z).
+assertEq(set.size, 1);  // Elements 0 to 24 are removed, leaving only 25 (Z).
 assertEq(set.has('Z'), true);
diff --git a/js/src/jit-test/tests/collections/Set-iterator-remove-6.js b/js/src/jit-test/tests/collections/Set-iterator-remove-6.js
index 1e03c0fccdc7..d21b19500783 100644
--- a/js/src/jit-test/tests/collections/Set-iterator-remove-6.js
+++ b/js/src/jit-test/tests/collections/Set-iterator-remove-6.js
@@ -11,7 +11,7 @@ var iter = set.iterator();
 assertEq(iter.next(), 0);
 for (var i = 0; i < 30; i++)
     set.delete(i);
-assertEq(set.size(), 2);
+assertEq(set.size, 2);
 for (var i = 32; i < 100; i++)
     set.add(i);  // eventually triggers compaction
 
diff --git a/js/src/jit-test/tests/collections/Set-size.js b/js/src/jit-test/tests/collections/Set-size.js
index b82c24e96a71..fc1c266dd50f 100644
--- a/js/src/jit-test/tests/collections/Set-size.js
+++ b/js/src/jit-test/tests/collections/Set-size.js
@@ -3,5 +3,5 @@
 var s1 = Set(), s2 = Set();
 for (var i = 0; i < 30; i++)
     s1.add(i);
-assertEq(s1.size(), 30);
-assertEq(s2.size(), 0);
+assertEq(s1.size, 30);
+assertEq(s2.size, 0);
diff --git a/js/src/jit-test/tests/collections/Set-surfaces-1.js b/js/src/jit-test/tests/collections/Set-surfaces-1.js
index 5b31e1a21463..fe44883d026b 100644
--- a/js/src/jit-test/tests/collections/Set-surfaces-1.js
+++ b/js/src/jit-test/tests/collections/Set-surfaces-1.js
@@ -30,4 +30,11 @@ function checkMethod(name, arity) {
 checkMethod("has", 1);
 checkMethod("add", 1);
 checkMethod("delete", 1);
+
+var desc = Object.getOwnPropertyDescriptor(Set.prototype, "size");
+assertEq(desc.enumerable, false);
+assertEq(desc.configurable, true);
+assertEq(typeof desc.get, 'function');
+assertEq(desc.get.length, 0);
+assertEq(desc.set, undefined);
 checkMethod("clear", 0);
diff --git a/js/src/jit-test/tests/collections/Set-surfaces-2.js b/js/src/jit-test/tests/collections/Set-surfaces-2.js
index 05fc4920e993..20ab6a32e6fa 100644
--- a/js/src/jit-test/tests/collections/Set-surfaces-2.js
+++ b/js/src/jit-test/tests/collections/Set-surfaces-2.js
@@ -8,11 +8,14 @@ function testcase(obj, fn) {
     assertThrowsInstanceOf(function () { fn.apply(obj, args); }, TypeError);
 }
 
+var Set_size_getter = Object.getOwnPropertyDescriptor(Set.prototype, "size").get;
+
 function test(obj) {
     testcase(obj, Set.prototype.has, 12);
     testcase(obj, Set.prototype.add, 12);
     testcase(obj, Set.prototype.delete, 12);
     testcase(obj, Set.prototype.clear);
+    testcase(obj, Set_size_getter);
 }
 
 test(Set.prototype);
diff --git a/js/src/jit-test/tests/collections/bug-743101.js b/js/src/jit-test/tests/collections/bug-743101.js
index d30f3fc4e03c..30c563f5ad5e 100644
--- a/js/src/jit-test/tests/collections/bug-743101.js
+++ b/js/src/jit-test/tests/collections/bug-743101.js
@@ -1,5 +1,7 @@
 load(libdir + "asserts.js");
 
 var g = newGlobal('new-compartment');
-assertThrowsInstanceOf(function () { Map.prototype.size.apply(g, []); }, g.TypeError);
-assertThrowsInstanceOf(function () { Set.prototype.size.apply(g, []); }, g.TypeError);
+for (var cls of [Map, Set]) {
+    var getter = Object.getOwnPropertyDescriptor(cls.prototype, "size").get;
+    assertThrowsInstanceOf(function () { getter.apply(g, []); }, g.TypeError);
+}
diff --git a/services/common/tests/unit/test_aitc_server.js b/services/common/tests/unit/test_aitc_server.js
index f8cdd4d16f3a..032c3cd89b25 100644
--- a/services/common/tests/unit/test_aitc_server.js
+++ b/services/common/tests/unit/test_aitc_server.js
@@ -158,7 +158,7 @@ add_test(function test_invalid_request_method() {
       allowed.add(method);
     }
 
-    do_check_eq(allowed.size(), 3);
+    do_check_eq(allowed.size, 3);
     for (let method of ["GET", "PUT", "DELETE"]) {
       do_check_true(allowed.has(method));
     }
diff --git a/toolkit/components/contentprefs/nsContentPrefService.js b/toolkit/components/contentprefs/nsContentPrefService.js
index 4dc9d4f09c3e..e50765ed3736 100644
--- a/toolkit/components/contentprefs/nsContentPrefService.js
+++ b/toolkit/components/contentprefs/nsContentPrefService.js
@@ -131,7 +131,7 @@ var inMemoryPrefsProto = {
 
     if (this._prefCache[aGroup].has(aName)) {
       this._prefCache[aGroup].delete(aName);
-      if (this._prefCache[aGroup].size() == 0) {
+      if (this._prefCache[aGroup].size == 0) {
         // remove empty group
         delete this._prefCache[aGroup];
       }
diff --git a/toolkit/mozapps/plugins/content/pluginInstallerWizard.js b/toolkit/mozapps/plugins/content/pluginInstallerWizard.js
index d16479fa73cd..9271f5b988b4 100644
--- a/toolkit/mozapps/plugins/content/pluginInstallerWizard.js
+++ b/toolkit/mozapps/plugins/content/pluginInstallerWizard.js
@@ -78,9 +78,9 @@ nsPluginInstallerWizard.prototype.pluginInfoReceived = function (aPluginRequestI
     progressMeter.setAttribute("mode", "determined");
 
   progressMeter.setAttribute("value",
-      ((this.WSPluginCounter / this.mPluginRequests.size()) * 100) + "%");
+      ((this.WSPluginCounter / this.mPluginRequests.size) * 100) + "%");
 
-  if (this.WSPluginCounter == this.mPluginRequests.size()) {
+  if (this.WSPluginCounter == this.mPluginRequests.size) {
     // check if no plugins were found
     if (this.mPluginInfoArrayLength == 0) {
       this.advancePage("lastpage");