diff --git a/packages/ember-metal/lib/properties.js b/packages/ember-metal/lib/properties.js
index f9cf96291d0..265c754343b 100644
--- a/packages/ember-metal/lib/properties.js
+++ b/packages/ember-metal/lib/properties.js
@@ -162,8 +162,12 @@ if (EMBER_METAL_ES5_GETTERS) {
   }
 
   DESCRIPTOR_GETTER_FUNCTION = function(name, descriptor) {
+    let trap;
     return function CPGETTER_FUNCTION() {
-      return trapFor(this, name, descriptor);
+      if (trap) { return trap; }
+
+      trap = trapFor(this, name, descriptor);
+      return trap;
     };
   };
 }
@@ -231,6 +235,18 @@ export function defineProperty(obj, keyName, desc, data, meta) {
     }
   }
 
+  // used to track if the the property being defined be enumerable
+  let enumerable = true;
+
+  // Ember.NativeArray is a normal Ember.Mixin that we mix into `Array.prototype` when prototype extensions are enabled
+  // mutating a native object prototype like this should _not_ result in enumerable properties being added (or we have significant
+  // issues with things like deep equality checks from test frameworks, or things like jQuery.extend(true, [], [])).
+  //
+  // this is a hack, and we should stop mutating the array prototype by default 😫
+  if (obj === Array.prototype) {
+    enumerable = false;
+  }
+
   let value;
   if (desc instanceof Descriptor) {
     value = desc;
@@ -238,16 +254,23 @@ export function defineProperty(obj, keyName, desc, data, meta) {
     if (EMBER_METAL_ES5_GETTERS || DESCRIPTOR_TRAP) {
       Object.defineProperty(obj, keyName, {
         configurable: true,
-        enumerable: true,
+        enumerable,
         get: DESCRIPTOR_GETTER_FUNCTION(keyName, value)
       });
     } else if (MANDATORY_SETTER && watching) {
       Object.defineProperty(obj, keyName, {
         configurable: true,
-        enumerable: true,
+        enumerable,
         writable: true,
         value
       });
+    } else if (enumerable === false) {
+      Object.defineProperty(obj, keyName, {
+        configurable: true,
+        writable: true,
+        enumerable,
+        value
+      });
     } else {
       obj[keyName] = value;
     }
@@ -267,7 +290,7 @@ export function defineProperty(obj, keyName, desc, data, meta) {
 
       let defaultDescriptor = {
         configurable: true,
-        enumerable: true,
+        enumerable,
         set: MANDATORY_SETTER_FUNCTION(keyName),
         get: DEFAULT_GETTER_FUNCTION(keyName)
       };
@@ -276,7 +299,14 @@ export function defineProperty(obj, keyName, desc, data, meta) {
     } else if ((EMBER_METAL_ES5_GETTERS || DESCRIPTOR_TRAP) && wasDescriptor) {
       Object.defineProperty(obj, keyName, {
         configurable: true,
-        enumerable: true,
+        enumerable,
+        writable: true,
+        value
+      });
+    } else if (enumerable === false) {
+      Object.defineProperty(obj, keyName, {
+        configurable: true,
+        enumerable,
         writable: true,
         value
       });
diff --git a/packages/ember-runtime/lib/ext/function.js b/packages/ember-runtime/lib/ext/function.js
index cc3d39e1311..71991095333 100644
--- a/packages/ember-runtime/lib/ext/function.js
+++ b/packages/ember-runtime/lib/ext/function.js
@@ -78,9 +78,14 @@ if (ENV.EXTEND_PROTOTYPES.Function) {
     @for Function
     @public
   */
-  FunctionPrototype.property = function () {
-    return computed(...arguments, this);
-  };
+  Object.defineProperty(FunctionPrototype, 'property', {
+    configurable: true,
+    enumerable: false,
+    writable: true,
+    value: function () {
+      return computed(...arguments, this);
+    }
+  });
 
   /**
     The `observes` extension of Javascript's Function prototype is available
@@ -109,28 +114,37 @@ if (ENV.EXTEND_PROTOTYPES.Function) {
     @for Function
     @public
   */
-  FunctionPrototype.observes = function() {
-    return observer(...arguments, this);
-  };
-
-
-  FunctionPrototype._observesImmediately = function () {
-    assert(
-      'Immediate observers must observe internal properties only, ' +
-      'not properties on other objects.',
-      function checkIsInternalProperty() {
-        for (let i = 0; i < arguments.length; i++) {
-          if (arguments[i].indexOf('.') !== -1) {
-            return false;
+  Object.defineProperty(FunctionPrototype, 'observes', {
+    configurable: true,
+    enumerable: false,
+    writable: true,
+    value: function () {
+      return observer(...arguments, this);
+    }
+  });
+
+  Object.defineProperty(FunctionPrototype, '_observesImmediately', {
+    configurable: true,
+    enumerable: false,
+    writable: true,
+    value: function () {
+      assert(
+        'Immediate observers must observe internal properties only, ' +
+        'not properties on other objects.',
+        function checkIsInternalProperty() {
+          for (let i = 0; i < arguments.length; i++) {
+            if (arguments[i].indexOf('.') !== -1) {
+              return false;
+            }
           }
+          return true;
         }
-        return true;
-      }
-    );
+      );
 
-    // observes handles property expansion
-    return this.observes(...arguments);
-  };
+      // observes handles property expansion
+      return this.observes(...arguments);
+    }
+  });
 
   /**
     The `on` extension of Javascript's Function prototype is available
@@ -156,7 +170,13 @@ if (ENV.EXTEND_PROTOTYPES.Function) {
     @for Function
     @public
   */
-  FunctionPrototype.on = function () {
-    return on(...arguments, this);
-  };
+
+  Object.defineProperty(FunctionPrototype, 'on', {
+    configurable: true,
+    enumerable: false,
+    writable: true,
+    value: function () {
+      return on(...arguments, this);
+    }
+  });
 }
diff --git a/packages/ember-runtime/lib/ext/string.js b/packages/ember-runtime/lib/ext/string.js
index ffc03ccfed6..dc05fa46ee7 100644
--- a/packages/ember-runtime/lib/ext/string.js
+++ b/packages/ember-runtime/lib/ext/string.js
@@ -25,9 +25,14 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.w = function () {
-    return w(this);
-  };
+  Object.defineProperty(StringPrototype, 'w', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function() {
+      return w(this);
+    }
+  });
 
   /**
     See [String.loc](/api/ember/release/classes/String/methods/loc?anchor=loc).
@@ -37,9 +42,14 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.loc = function (...args) {
-    return loc(this, args);
-  };
+  Object.defineProperty(StringPrototype, 'loc', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function(...args) {
+      return loc(this, args);
+    }
+  });
 
   /**
     See [String.camelize](/api/ember/release/classes/String/methods/camelize?anchor=camelize).
@@ -49,9 +59,14 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.camelize = function () {
-    return camelize(this);
-  };
+  Object.defineProperty(StringPrototype, 'camelize', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function() {
+      return camelize(this);
+    }
+  });
 
   /**
     See [String.decamelize](/api/ember/release/classes/String/methods/decamelize?anchor=decamelize).
@@ -61,9 +76,14 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.decamelize = function () {
-    return decamelize(this);
-  };
+  Object.defineProperty(StringPrototype, 'decamelize', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function() {
+      return decamelize(this);
+    }
+  });
 
   /**
     See [String.dasherize](/api/ember/release/classes/String/methods/dasherize?anchor=dasherize).
@@ -73,9 +93,14 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.dasherize = function () {
-    return dasherize(this);
-  };
+  Object.defineProperty(StringPrototype, 'dasherize', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function() {
+      return dasherize(this);
+    }
+  });
 
   /**
     See [String.underscore](/api/ember/release/classes/String/methods/underscore?anchor=underscore).
@@ -85,9 +110,14 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.underscore = function () {
-    return underscore(this);
-  };
+  Object.defineProperty(StringPrototype, 'underscore', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function() {
+      return underscore(this);
+    }
+  });
 
   /**
     See [String.classify](/api/ember/release/classes/String/methods/classify?anchor=classify).
@@ -97,9 +127,14 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.classify = function () {
-    return classify(this);
-  };
+  Object.defineProperty(StringPrototype, 'classify', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function() {
+      return classify(this);
+    }
+  });
 
   /**
     See [String.capitalize](/api/ember/release/classes/String/methods/capitalize?anchor=capitalize).
@@ -109,7 +144,12 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     @static
     @private
   */
-  StringPrototype.capitalize = function () {
-    return capitalize(this);
-  };
+  Object.defineProperty(StringPrototype, 'capitalize', {
+    configurable: true,
+    enumerable: false,
+    writeable: true,
+    value: function() {
+      return capitalize(this);
+    }
+  });
 }