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diff --git a/toolkit/jetpack/sdk/lang/functional/concurrent.js b/toolkit/jetpack/sdk/lang/functional/concurrent.js
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+++ b/toolkit/jetpack/sdk/lang/functional/concurrent.js
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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/. */
+
+// Disclaimer: Some of the functions in this module implement APIs from
+// Jeremy Ashkenas's http://underscorejs.org/ library and all credits for
+// those goes to him.
+
+"use strict";
+
+module.metadata = {
+  "stability": "unstable"
+};
+
+const { arity, name, derive, invoke } = require("./helpers");
+const { setTimeout, clearTimeout, setImmediate } = require("../../timers");
+
+/**
+ * Takes a function and returns a wrapped one instead, calling which will call
+ * original function in the next turn of event loop. This is basically utility
+ * to do `setImmediate(function() { ... })`, with a difference that returned
+ * function is reused, instead of creating a new one each time. This also allows
+ * to use this functions as event listeners.
+ */
+const defer = f => derive(function(...args) {
+  setImmediate(invoke, f, args, this);
+}, f);
+exports.defer = defer;
+// Exporting `remit` alias as `defer` may conflict with promises.
+exports.remit = defer;
+
+/**
+ * Much like setTimeout, invokes function after wait milliseconds. If you pass
+ * the optional arguments, they will be forwarded on to the function when it is
+ * invoked.
+ */
+const delay = function delay(f, ms, ...args) {
+  setTimeout(() => f.apply(this, args), ms);
+};
+exports.delay = delay;
+
+/**
+ * From underscore's `_.debounce`
+ * http://underscorejs.org
+ * (c) 2009-2014 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+ * Underscore may be freely distributed under the MIT license.
+ */
+const debounce = function debounce (fn, wait) {
+  let timeout, args, context, timestamp, result;
+
+  let later = function () {
+    let last = Date.now() - timestamp;
+    if (last < wait) {
+      timeout = setTimeout(later, wait - last);
+    } else {
+      timeout = null;
+      result = fn.apply(context, args);
+      context = args = null;
+    }
+  };
+
+  return function (...aArgs) {
+    context = this;
+    args = aArgs;
+    timestamp  = Date.now();
+    if (!timeout) {
+      timeout = setTimeout(later, wait);
+    }
+
+    return result;
+  };
+};
+exports.debounce = debounce;
+
+/**
+ * From underscore's `_.throttle`
+ * http://underscorejs.org
+ * (c) 2009-2014 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+ * Underscore may be freely distributed under the MIT license.
+ */
+const throttle = function throttle (func, wait, options) {
+  let context, args, result;
+  let timeout = null;
+  let previous = 0;
+  options || (options = {});
+  let later = function() {
+    previous = options.leading === false ? 0 : Date.now();
+    timeout = null;
+    result = func.apply(context, args);
+    context = args = null;
+  };
+  return function() {
+    let now = Date.now();
+    if (!previous && options.leading === false) previous = now;
+    let remaining = wait - (now - previous);
+    context = this;
+    args = arguments;
+    if (remaining <= 0) {
+      clearTimeout(timeout);
+      timeout = null;
+      previous = now;
+      result = func.apply(context, args);
+      context = args = null;
+    } else if (!timeout && options.trailing !== false) {
+      timeout = setTimeout(later, remaining);
+    }
+    return result;
+  };
+};
+exports.throttle = throttle;