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diff --git a/toolkit/modules/ObjectUtils.jsm b/toolkit/modules/ObjectUtils.jsm
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+/* 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/. */
+
+// Portions of this file are originally from narwhal.js (http://narwhaljs.org)
+// Copyright (c) 2009 Thomas Robinson <280north.com>
+// MIT license: http://opensource.org/licenses/MIT
+
+"use strict";
+
+var EXPORTED_SYMBOLS = ["ObjectUtils"];
+
+// Used only to cause test failures.
+
+var pSlice = Array.prototype.slice;
+
+var ObjectUtils = {
+  /**
+   * This tests objects & values for deep equality.
+   *
+   * We check using the most exact approximation of equality between two objects
+   * to keep the chance of false positives to a minimum.
+   * `JSON.stringify` is not designed to be used for this purpose; objects may
+   * have ambiguous `toJSON()` implementations that would influence the test.
+   *
+   * @param a (mixed) Object or value to be compared.
+   * @param b (mixed) Object or value to be compared.
+   * @return Boolean Whether the objects are deep equal.
+   */
+  deepEqual(a, b) {
+    return _deepEqual(a, b);
+  },
+
+  /**
+   * A thin wrapper on an object, designed to prevent client code from
+   * accessing non-existent properties because of typos.
+   *
+   * // Without `strict`
+   * let foo = { myProperty: 1 };
+   * foo.MyProperty; // undefined
+   *
+   * // With `strict`
+   * let strictFoo = ObjectUtils.strict(foo);
+   * strictFoo.myProperty; // 1
+   * strictFoo.MyProperty; // TypeError: No such property "MyProperty"
+   *
+   * Note that `strict` has no effect in non-DEBUG mode.
+   */
+  strict(obj) {
+    return _strict(obj);
+  },
+
+  /**
+   * Returns `true` if `obj` is an array without elements, an object without
+   * enumerable properties, or a falsy primitive; `false` otherwise.
+   */
+  isEmpty(obj) {
+    if (!obj) {
+      return true;
+    }
+    if (typeof obj != "object") {
+      return false;
+    }
+    if (Array.isArray(obj)) {
+      return !obj.length;
+    }
+    for (let key in obj) {
+      return false;
+    }
+    return true;
+  },
+};
+
+// ... Start of previously MIT-licensed code.
+// This deepEqual implementation is originally from narwhal.js (http://narwhaljs.org)
+// Copyright (c) 2009 Thomas Robinson <280north.com>
+// MIT license: http://opensource.org/licenses/MIT
+
+function _deepEqual(a, b) {
+  // The numbering below refers to sections in the CommonJS spec.
+
+  // 7.1 All identical values are equivalent, as determined by ===.
+  if (a === b) {
+    return true;
+    // 7.2 If the b value is a Date object, the a value is
+    // equivalent if it is also a Date object that refers to the same time.
+  }
+  let aIsDate = instanceOf(a, "Date");
+  let bIsDate = instanceOf(b, "Date");
+  if (aIsDate || bIsDate) {
+    if (!aIsDate || !bIsDate) {
+      return false;
+    }
+    if (isNaN(a.getTime()) && isNaN(b.getTime())) {
+      return true;
+    }
+    return a.getTime() === b.getTime();
+    // 7.3 If the b value is a RegExp object, the a value is
+    // equivalent if it is also a RegExp object with the same source and
+    // properties (`global`, `multiline`, `lastIndex`, `ignoreCase`).
+  }
+  let aIsRegExp = instanceOf(a, "RegExp");
+  let bIsRegExp = instanceOf(b, "RegExp");
+  if (aIsRegExp || bIsRegExp) {
+    return (
+      aIsRegExp &&
+      bIsRegExp &&
+      a.source === b.source &&
+      a.global === b.global &&
+      a.multiline === b.multiline &&
+      a.lastIndex === b.lastIndex &&
+      a.ignoreCase === b.ignoreCase
+    );
+    // 7.4 Other pairs that do not both pass typeof value == "object",
+    // equivalence is determined by ==.
+  }
+  if (typeof a != "object" || typeof b != "object") {
+    return a == b;
+  }
+  // 7.5 For all other Object pairs, including Array objects, equivalence is
+  // determined by having the same number of owned properties (as verified
+  // with Object.prototype.hasOwnProperty.call), the same set of keys
+  // (although not necessarily the same order), equivalent values for every
+  // corresponding key, and an identical 'prototype' property. Note: this
+  // accounts for both named and indexed properties on Arrays.
+  return objEquiv(a, b);
+}
+
+function instanceOf(object, type) {
+  return Object.prototype.toString.call(object) == "[object " + type + "]";
+}
+
+function isUndefinedOrNull(value) {
+  return value === null || value === undefined;
+}
+
+function isArguments(object) {
+  return instanceOf(object, "Arguments");
+}
+
+function objEquiv(a, b) {
+  if (isUndefinedOrNull(a) || isUndefinedOrNull(b)) {
+    return false;
+  }
+  // An identical 'prototype' property.
+  if ((a.prototype || undefined) != (b.prototype || undefined)) {
+    return false;
+  }
+  // Object.keys may be broken through screwy arguments passing. Converting to
+  // an array solves the problem.
+  if (isArguments(a)) {
+    if (!isArguments(b)) {
+      return false;
+    }
+    a = pSlice.call(a);
+    b = pSlice.call(b);
+    return _deepEqual(a, b);
+  }
+  let ka, kb;
+  try {
+    ka = Object.keys(a);
+    kb = Object.keys(b);
+  } catch (e) {
+    // Happens when one is a string literal and the other isn't
+    return false;
+  }
+  // Having the same number of owned properties (keys incorporates
+  // hasOwnProperty)
+  if (ka.length != kb.length) {
+    return false;
+  }
+  // The same set of keys (although not necessarily the same order),
+  ka.sort();
+  kb.sort();
+  // Equivalent values for every corresponding key, and possibly expensive deep
+  // test
+  for (let key of ka) {
+    if (!_deepEqual(a[key], b[key])) {
+      return false;
+    }
+  }
+  return true;
+}
+
+// ... End of previously MIT-licensed code.
+
+function _strict(obj) {
+  if (typeof obj != "object") {
+    throw new TypeError("Expected an object");
+  }
+
+  return new Proxy(obj, {
+    get(target, name) {
+      if (name in obj) {
+        return obj[name];
+      }
+
+      let error = new TypeError(`No such property: "${name}"`);
+      Promise.reject(error); // Cause an xpcshell/mochitest failure.
+      throw error;
+    },
+  });
+}