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diff --git a/toolkit/modules/PromiseUtils.sys.mjs b/toolkit/modules/PromiseUtils.sys.mjs
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+++ b/toolkit/modules/PromiseUtils.sys.mjs
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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/. */
+
+export var PromiseUtils = {
+  /*
+   * Creates a new pending Promise and provide methods to resolve and reject this Promise.
+   *
+   * @return {Deferred} an object consisting of a pending Promise "promise"
+   * and methods "resolve" and "reject" to change its state.
+   */
+  defer() {
+    return new Deferred();
+  },
+
+  /**
+   * Requests idle dispatch to the main thread for the given callback,
+   * and returns a promise which resolves to the callback's return value
+   * when it has been executed.
+   *
+   * @param {function} callback
+   * @param {integer} [timeout]
+   *        An optional timeout, after which the callback will be
+   *        executed immediately if idle dispatch has not yet occurred.
+   *
+   * @returns {Promise}
+   */
+  idleDispatch(callback, timeout = 0) {
+    return new Promise((resolve, reject) => {
+      Services.tm.idleDispatchToMainThread(() => {
+        try {
+          resolve(callback());
+        } catch (e) {
+          reject(e);
+        }
+      }, timeout);
+    });
+  },
+};
+
+/**
+ * The definition of Deferred object which is returned by PromiseUtils.defer(),
+ * It contains a Promise and methods to resolve/reject it.
+ */
+function Deferred() {
+  /* A method to resolve the associated Promise with the value passed.
+   * If the promise is already settled it does nothing.
+   *
+   * @param {anything} value : This value is used to resolve the promise
+   * If the value is a Promise then the associated promise assumes the state
+   * of Promise passed as value.
+   */
+  this.resolve = null;
+
+  /* A method to reject the assocaited Promise with the value passed.
+   * If the promise is already settled it does nothing.
+   *
+   * @param {anything} reason: The reason for the rejection of the Promise.
+   * Generally its an Error object. If however a Promise is passed, then the Promise
+   * itself will be the reason for rejection no matter the state of the Promise.
+   */
+  this.reject = null;
+
+  /* A newly created Pomise object.
+   * Initially in pending state.
+   */
+  this.promise = new Promise((resolve, reject) => {
+    this.resolve = resolve;
+    this.reject = reject;
+  });
+}