deleted file mode 100644
--- a/services/common/modules-testing/utils.js
+++ /dev/null
@@ -1,42 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-"use strict";
-
-this.EXPORTED_SYMBOLS = [
-  "TestingUtils",
-];
-
-this.TestingUtils = {
-  /**
-   * Perform a deep copy of an Array or Object.
-   */
-  deepCopy: function deepCopy(thing, noSort) {
-    if (typeof(thing) != "object" || thing == null) {
-      return thing;
-    }
-
-    if (Array.isArray(thing)) {
-      let ret = [];
-      for (let element of thing) {
-        ret.push(this.deepCopy(element, noSort));
-      }
-
-      return ret;
-    }
-
-    let ret = {};
-    let props = Object.keys(thing);
-
-    if (!noSort) {
-      props = props.sort();
-    }
-
-    for (let prop of props) {
-      ret[prop] = this.deepCopy(thing[prop], noSort);
-    }
-
-    return ret;
-  },
-};

--- a/services/common/moz.build
+++ b/services/common/moz.build
@@ -35,15 +35,14 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] != 'andr
     ]
 
     TESTING_JS_MODULES.services.common += [
         'modules-testing/storageserver.js',
     ]
 
 TESTING_JS_MODULES.services.common += [
     'modules-testing/logging.js',
-    'modules-testing/utils.js',
 ]
 
 JS_PREFERENCE_FILES += [
     'services-common.js',
 ]
 

deleted file mode 100644
--- a/services/common/tests/unit/test_utils_deepCopy.js
+++ /dev/null
@@ -1,18 +0,0 @@
-/* Any copyright is dedicated to the Public Domain.
-   http://creativecommons.org/publicdomain/zero/1.0/ */
-
-Cu.import("resource://testing-common/services/common/utils.js");
-
-function run_test() {
-  let thing = {o: {foo: "foo", bar: ["bar"]}, a: ["foo", {bar: "bar"}]};
-  let ret = TestingUtils.deepCopy(thing);
-  do_check_neq(ret, thing)
-  do_check_neq(ret.o, thing.o);
-  do_check_neq(ret.o.bar, thing.o.bar);
-  do_check_neq(ret.a, thing.a);
-  do_check_neq(ret.a[1], thing.a[1]);
-  do_check_eq(ret.o.foo, thing.o.foo);
-  do_check_eq(ret.o.bar[0], thing.o.bar[0]);
-  do_check_eq(ret.a[0], thing.a[0]);
-  do_check_eq(ret.a[1].bar, thing.a[1].bar);
-}

--- a/services/common/tests/unit/xpcshell.ini
+++ b/services/common/tests/unit/xpcshell.ini
@@ -26,17 +26,16 @@ tags = blocklist
 [test_storage_adapter.js]
 tags = blocklist
 [test_storage_adapter_shutdown.js]
 tags = blocklist
 
 [test_utils_atob.js]
 [test_utils_convert_string.js]
 [test_utils_dateprefs.js]
-[test_utils_deepCopy.js]
 [test_utils_encodeBase32.js]
 [test_utils_encodeBase64URL.js]
 [test_utils_ensureMillisecondsTimestamp.js]
 [test_utils_json.js]
 [test_utils_makeURI.js]
 [test_utils_namedTimer.js]
 [test_utils_sets.js]
 [test_utils_utf8.js]

--- a/services/sync/tests/unit/head_helpers.js
+++ b/services/sync/tests/unit/head_helpers.js
@@ -7,17 +7,16 @@
 /* import-globals-from head_http_server.js */
 
 // This file expects Service to be defined in the global scope when EHTestsCommon
 // is used (from service.js).
 /* global Service */
 
 Cu.import("resource://services-common/async.js");
 Cu.import("resource://services-common/utils.js");
-Cu.import("resource://testing-common/services/common/utils.js");
 Cu.import("resource://testing-common/PlacesTestUtils.jsm");
 Cu.import("resource://services-sync/util.js");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/PlacesUtils.jsm");
 Cu.import("resource://gre/modules/ObjectUtils.jsm");
 
 add_task(async function head_setup() {
   // If a test imports Service, make sure it is initialized first.
@@ -234,24 +233,24 @@ function mockGetWindowEnumerator(url, nu
       mockIsPrivate: false,
       gBrowser: {
         tabs,
       },
     };
     elements.push(win);
 
     for (let t = 0; t < numTabs; ++t) {
-      tabs.push(TestingUtils.deepCopy({
+      tabs.push(Cu.cloneInto({
         index: indexes ? indexes() : 1,
         entries: (moreURLs ? [url].concat(moreURLs()) : [url]).map(url2entry),
         attributes: {
           image: "image"
         },
         lastAccessed: 1499
-      }));
+      }, {}));
     }
   }
 
   // Always include a closed window and a private window.
   elements.push({
     closed: true,
     mockIsPrivate: false,
     gBrowser: {

--- a/services/sync/tests/unit/test_bookmark_livemarks.js
+++ b/services/sync/tests/unit/test_bookmark_livemarks.js
@@ -2,17 +2,16 @@
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
 Cu.import("resource://gre/modules/Log.jsm");
 Cu.import("resource://services-sync/record.js");
 Cu.import("resource://services-sync/engines.js");
 Cu.import("resource://services-sync/engines/bookmarks.js");
 Cu.import("resource://services-sync/util.js");
 Cu.import("resource://services-sync/service.js");
-Cu.import("resource://testing-common/services/common/utils.js");
 
 const DESCRIPTION_ANNO = "bookmarkProperties/description";
 
 let engine;
 let store;
 
 // Record borrowed from Bug 631361.
 const record631361 = {
@@ -50,17 +49,17 @@ const record631361 = {
       "mNTdpgoRZMbW", "-L8Vci6CbkJY", "bVzudKSQERc1", "Gxl9lb4DXsmL",
       "3Qr13GucOtEh"]},
   collection: "bookmarks"
 };
 
 function makeLivemark(p, mintGUID) {
   let b = new Livemark("bookmarks", p.id);
   // Copy here, because tests mutate the contents.
-  b.cleartext = TestingUtils.deepCopy(p);
+  b.cleartext = Cu.cloneInto(p, {});
 
   if (mintGUID)
     b.id = Utils.makeGUID();
 
   return b;
 }
 
 add_task(async function setup() {

--- a/services/sync/tests/unit/test_tab_store.js
+++ b/services/sync/tests/unit/test_tab_store.js
@@ -1,15 +1,14 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
 Cu.import("resource://services-sync/engines/tabs.js");
 Cu.import("resource://services-sync/service.js");
 Cu.import("resource://services-sync/util.js");
-Cu.import("resource://testing-common/services/common/utils.js");
 
 async function getMockStore() {
   let engine = new TabEngine(Service);
   await engine.initialize();
   let store = engine._store;
   store.getTabState = mockGetTabState;
   store.shouldSkipWindow = mockShouldSkipWindow;
   return store;