--- a/browser/devtools/shared/test/head.js
+++ b/browser/devtools/shared/test/head.js
@@ -30,19 +30,18 @@ function addTab(aURL, aCallback)
     browser.removeEventListener("load", onTabLoad, true);
     aCallback(browser, tab, browser.contentDocument);
   }
 
   browser.addEventListener("load", onTabLoad, true);
 }
 
 function promiseTab(aURL) {
-  let deferred = Promise.defer();
-  addTab(aURL, deferred.resolve);
-  return deferred.promise;
+  return new Promise(resolve =>
+    addTab(aURL, resolve));
 }
 
 registerCleanupFunction(function tearDown() {
   while (gBrowser.tabs.length > 1) {
     gBrowser.removeCurrentTab();
   }
 
   console = undefined;
@@ -133,16 +132,16 @@ function oneTimeObserve(name, callback) 
   };
   Services.obs.addObserver(func, name, false);
 }
 
 function* createHost(type = "bottom", src = "data:text/html;charset=utf-8,") {
   let host = new Hosts[type](gBrowser.selectedTab);
   let iframe = yield host.create();
 
-  let loaded = Promise.defer();
-  let domHelper = new DOMHelpers(iframe.contentWindow);
-  iframe.setAttribute("src", src);
-  domHelper.onceDOMReady(loaded.resolve);
-  yield loaded.promise;
+  yield new Promise(resolve => {
+    let domHelper = new DOMHelpers(iframe.contentWindow);
+    iframe.setAttribute("src", src);
+    domHelper.onceDOMReady(resolve);
+  });
 
   return [host, iframe.contentWindow, iframe.contentDocument];
 }

--- a/toolkit/devtools/server/tests/browser/browser_storage_dynamic_windows.js
+++ b/toolkit/devtools/server/tests/browser/browser_storage_dynamic_windows.js
@@ -123,187 +123,187 @@ function markOutMatched(toBeEmptied, dat
   }
 }
 
 function testReload() {
   info("Testing if reload works properly");
 
   let shouldBeEmptyFirst = Cu.cloneInto(beforeReload,  {});
   let shouldBeEmptyLast = Cu.cloneInto(beforeReload,  {});
-  let reloaded = Promise.defer();
+  return new Promise(resolve => {
 
-  let onStoresUpdate = data => {
-    info("in stores update of testReload");
-    // This might be second time stores update is happening, in which case,
-    // data.deleted will be null.
-    // OR.. This might be the first time on a super slow machine where both
-    // data.deleted and data.added is missing in the first update.
-    if (data.deleted) {
-      markOutMatched(shouldBeEmptyFirst, data.deleted, true);
-    }
+    let onStoresUpdate = data => {
+      info("in stores update of testReload");
+      // This might be second time stores update is happening, in which case,
+      // data.deleted will be null.
+      // OR.. This might be the first time on a super slow machine where both
+      // data.deleted and data.added is missing in the first update.
+      if (data.deleted) {
+        markOutMatched(shouldBeEmptyFirst, data.deleted, true);
+      }
 
-    if (!Object.keys(shouldBeEmptyFirst).length) {
-      info("shouldBeEmptyFirst is empty now");
-    }
+      if (!Object.keys(shouldBeEmptyFirst).length) {
+        info("shouldBeEmptyFirst is empty now");
+      }
 
-    // stores-update call might not have data.added for the first time on slow
-    // machines, in which case, data.added will be null
-    if (data.added) {
-      markOutMatched(shouldBeEmptyLast, data.added);
-    }
+      // stores-update call might not have data.added for the first time on slow
+      // machines, in which case, data.added will be null
+      if (data.added) {
+        markOutMatched(shouldBeEmptyLast, data.added);
+      }
 
-    if (!Object.keys(shouldBeEmptyLast).length) {
-      info("Everything to be received is received.");
-      endTestReloaded();
-    }
-  };
+      if (!Object.keys(shouldBeEmptyLast).length) {
+        info("Everything to be received is received.");
+        endTestReloaded();
+      }
+    };
 
-  let endTestReloaded = () => {
-    gFront.off("stores-update", onStoresUpdate);
-    reloaded.resolve();
-  };
+    let endTestReloaded = () => {
+      gFront.off("stores-update", onStoresUpdate);
+      resolve();
+    };
 
-  gFront.on("stores-update", onStoresUpdate);
+    gFront.on("stores-update", onStoresUpdate);
 
-  content.location.reload();
-  return reloaded.promise;
+    content.location.reload();
+  });
 }
 
 function testAddIframe() {
   info("Testing if new iframe addition works properly");
-  let reloaded = Promise.defer();
+  return new Promise(resolve => {
 
-  let shouldBeEmpty = {
-    localStorage: {
-      "https://sectest1.example.org": ["iframe-s-ls1"]
-    },
-    sessionStorage: {
-      "https://sectest1.example.org": ["iframe-s-ss1"]
-    },
-    cookies: {
-      "sectest1.example.org": ["sc1"]
-    },
-    indexedDB: {
-      // empty because indexed db creation happens after the page load, so at
-      // the time of window-ready, there was no indexed db present.
-      "https://sectest1.example.org": []
-    }
-  };
+    let shouldBeEmpty = {
+      localStorage: {
+        "https://sectest1.example.org": ["iframe-s-ls1"]
+      },
+      sessionStorage: {
+        "https://sectest1.example.org": ["iframe-s-ss1"]
+      },
+      cookies: {
+        "sectest1.example.org": ["sc1"]
+      },
+      indexedDB: {
+        // empty because indexed db creation happens after the page load, so at
+        // the time of window-ready, there was no indexed db present.
+        "https://sectest1.example.org": []
+      }
+    };
 
-  let onStoresUpdate = data => {
-    info("checking if the hosts list is correct for this iframe addition");
+    let onStoresUpdate = data => {
+      info("checking if the hosts list is correct for this iframe addition");
 
-    markOutMatched(shouldBeEmpty, data.added);
+      markOutMatched(shouldBeEmpty, data.added);
 
-    ok(!data.changed || !data.changed.cookies ||
-       !data.changed.cookies["https://sectest1.example.org"],
-       "Nothing got changed for cookies");
-    ok(!data.changed || !data.changed.localStorage ||
-       !data.changed.localStorage["https://sectest1.example.org"],
-       "Nothing got changed for local storage");
-    ok(!data.changed || !data.changed.sessionStorage ||
-       !data.changed.sessionStorage["https://sectest1.example.org"],
-       "Nothing got changed for session storage");
-    ok(!data.changed || !data.changed.indexedDB ||
-       !data.changed.indexedDB["https://sectest1.example.org"],
-       "Nothing got changed for indexed db");
+      ok(!data.changed || !data.changed.cookies ||
+         !data.changed.cookies["https://sectest1.example.org"],
+         "Nothing got changed for cookies");
+      ok(!data.changed || !data.changed.localStorage ||
+         !data.changed.localStorage["https://sectest1.example.org"],
+         "Nothing got changed for local storage");
+      ok(!data.changed || !data.changed.sessionStorage ||
+         !data.changed.sessionStorage["https://sectest1.example.org"],
+         "Nothing got changed for session storage");
+      ok(!data.changed || !data.changed.indexedDB ||
+         !data.changed.indexedDB["https://sectest1.example.org"],
+         "Nothing got changed for indexed db");
 
-    ok(!data.deleted || !data.deleted.cookies ||
-       !data.deleted.cookies["https://sectest1.example.org"],
-       "Nothing got deleted for cookies");
-    ok(!data.deleted || !data.deleted.localStorage ||
-       !data.deleted.localStorage["https://sectest1.example.org"],
-       "Nothing got deleted for local storage");
-    ok(!data.deleted || !data.deleted.sessionStorage ||
-       !data.deleted.sessionStorage["https://sectest1.example.org"],
-       "Nothing got deleted for session storage");
-    ok(!data.deleted || !data.deleted.indexedDB ||
-       !data.deleted.indexedDB["https://sectest1.example.org"],
-       "Nothing got deleted for indexed db");
+      ok(!data.deleted || !data.deleted.cookies ||
+         !data.deleted.cookies["https://sectest1.example.org"],
+         "Nothing got deleted for cookies");
+      ok(!data.deleted || !data.deleted.localStorage ||
+         !data.deleted.localStorage["https://sectest1.example.org"],
+         "Nothing got deleted for local storage");
+      ok(!data.deleted || !data.deleted.sessionStorage ||
+         !data.deleted.sessionStorage["https://sectest1.example.org"],
+         "Nothing got deleted for session storage");
+      ok(!data.deleted || !data.deleted.indexedDB ||
+         !data.deleted.indexedDB["https://sectest1.example.org"],
+         "Nothing got deleted for indexed db");
 
-    if (!Object.keys(shouldBeEmpty).length) {
-      info("Everything to be received is received.");
-      endTestReloaded();
-    }
-  };
+      if (!Object.keys(shouldBeEmpty).length) {
+        info("Everything to be received is received.");
+        endTestReloaded();
+      }
+    };
 
-  let endTestReloaded = () => {
-    gFront.off("stores-update", onStoresUpdate);
-    reloaded.resolve();
-  };
+    let endTestReloaded = () => {
+      gFront.off("stores-update", onStoresUpdate);
+      resolve();
+    };
 
-  gFront.on("stores-update", onStoresUpdate);
+    gFront.on("stores-update", onStoresUpdate);
 
-  let iframe = content.document.createElement("iframe");
-  iframe.src = ALT_DOMAIN_SECURED + "storage-secured-iframe.html";
-  content.document.querySelector("body").appendChild(iframe);
-  return reloaded.promise;
+    let iframe = content.document.createElement("iframe");
+    iframe.src = ALT_DOMAIN_SECURED + "storage-secured-iframe.html";
+    content.document.querySelector("body").appendChild(iframe);
+  });
 }
 
 function testRemoveIframe() {
   info("Testing if iframe removal works properly");
-  let reloaded = Promise.defer();
+  return new Promise(resolve => {
 
-  let shouldBeEmpty = {
-    localStorage: {
-      "http://sectest1.example.org": []
-    },
-    sessionStorage: {
-      "http://sectest1.example.org": []
-    }
-  };
+    let shouldBeEmpty = {
+      localStorage: {
+        "http://sectest1.example.org": []
+      },
+      sessionStorage: {
+        "http://sectest1.example.org": []
+      }
+    };
 
-  let onStoresUpdate = data => {
-    info("checking if the hosts list is correct for this iframe deletion");
+    let onStoresUpdate = data => {
+      info("checking if the hosts list is correct for this iframe deletion");
 
-    markOutMatched(shouldBeEmpty, data.deleted, true);
+      markOutMatched(shouldBeEmpty, data.deleted, true);
 
-    ok(!data.deleted.cookies || !data.deleted.cookies["sectest1.example.org"],
-       "Nothing got deleted for Cookies as the same hostname is still present");
+      ok(!data.deleted.cookies || !data.deleted.cookies["sectest1.example.org"],
+        "Nothing got deleted for Cookies as the same hostname is still present");
 
-    ok(!data.changed || !data.changed.cookies ||
-       !data.changed.cookies["http://sectest1.example.org"],
-       "Nothing got changed for cookies");
-    ok(!data.changed || !data.changed.localStorage ||
-       !data.changed.localStorage["http://sectest1.example.org"],
-       "Nothing got changed for local storage");
-    ok(!data.changed || !data.changed.sessionStorage ||
-       !data.changed.sessionStorage["http://sectest1.example.org"],
-       "Nothing got changed for session storage");
+      ok(!data.changed || !data.changed.cookies ||
+         !data.changed.cookies["http://sectest1.example.org"],
+         "Nothing got changed for cookies");
+      ok(!data.changed || !data.changed.localStorage ||
+         !data.changed.localStorage["http://sectest1.example.org"],
+         "Nothing got changed for local storage");
+      ok(!data.changed || !data.changed.sessionStorage ||
+         !data.changed.sessionStorage["http://sectest1.example.org"],
+         "Nothing got changed for session storage");
 
-    ok(!data.added || !data.added.cookies ||
-       !data.added.cookies["http://sectest1.example.org"],
-       "Nothing got added for cookies");
-    ok(!data.added || !data.added.localStorage ||
-       !data.added.localStorage["http://sectest1.example.org"],
-       "Nothing got added for local storage");
-    ok(!data.added || !data.added.sessionStorage ||
-       !data.added.sessionStorage["http://sectest1.example.org"],
-       "Nothing got added for session storage");
+      ok(!data.added || !data.added.cookies ||
+         !data.added.cookies["http://sectest1.example.org"],
+         "Nothing got added for cookies");
+      ok(!data.added || !data.added.localStorage ||
+         !data.added.localStorage["http://sectest1.example.org"],
+         "Nothing got added for local storage");
+      ok(!data.added || !data.added.sessionStorage ||
+         !data.added.sessionStorage["http://sectest1.example.org"],
+         "Nothing got added for session storage");
 
-    if (!Object.keys(shouldBeEmpty).length) {
-      info("Everything to be received is received.");
-      endTestReloaded();
+      if (!Object.keys(shouldBeEmpty).length) {
+        info("Everything to be received is received.");
+        endTestReloaded();
+      }
+    };
+
+    let endTestReloaded = () => {
+      gFront.off("stores-update", onStoresUpdate);
+      resolve();
+    };
+
+    gFront.on("stores-update", onStoresUpdate);
+
+    for (let iframe of content.document.querySelectorAll("iframe")) {
+      if (iframe.src.startsWith("http:")) {
+        iframe.remove();
+        break;
+      }
     }
-  };
-
-  let endTestReloaded = () => {
-    gFront.off("stores-update", onStoresUpdate);
-    reloaded.resolve();
-  };
-
-  gFront.on("stores-update", onStoresUpdate);
-
-  for (let iframe of content.document.querySelectorAll("iframe")) {
-    if (iframe.src.startsWith("http:")) {
-      iframe.remove();
-      break;
-    }
-  }
-  return reloaded.promise;
+  });
 }
 
 function test() {
   addTab(MAIN_DOMAIN + "storage-dynamic-windows.html").then(function(doc) {
     initDebuggerServer();
 
     let createConnection = () => {
       let client = new DebuggerClient(DebuggerServer.connectPipe());

--- a/toolkit/devtools/server/tests/browser/browser_timeline_actors.js
+++ b/toolkit/devtools/server/tests/browser/browser_timeline_actors.js
@@ -54,16 +54,15 @@ let test = asyncTest(function*() {
  *
  * @param function predicate
  *        Invoked once in a while until it returns true.
  * @param number interval [optional]
  *        How often the predicate is invoked, in milliseconds.
  */
 function waitUntil(predicate, interval = 10) {
   if (predicate()) {
-    return promise.resolve(true);
+    return Promise.resolve(true);
   }
-  let deferred = promise.defer();
-  setTimeout(function() {
-    waitUntil(predicate).then(() => deferred.resolve(true));
-  }, interval);
-  return deferred.promise;
+  return new Promise(resolve =>
+    setTimeout(function() {
+      waitUntil(predicate).then(() => resolve(true));
+    }, interval));
 }

--- a/toolkit/devtools/server/tests/browser/browser_timeline_iframes.js
+++ b/toolkit/devtools/server/tests/browser/browser_timeline_iframes.js
@@ -30,12 +30,11 @@ let test = asyncTest(function*() {
 
   info("Stop timeline marker recording");
   yield front.stop();
   yield closeDebuggerClient(client);
   gBrowser.removeCurrentTab();
 });
 
 function wait(ms) {
-  let def = promise.defer();
-  setTimeout(def.resolve, ms);
-  return def.promise;
+  return new Promise(resolve =>
+    setTimeout(resolve, ms));
 }

--- a/toolkit/devtools/server/tests/browser/head.js
+++ b/toolkit/devtools/server/tests/browser/head.js
@@ -3,17 +3,16 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cu = Components.utils;
 
 Cu.import("resource://gre/modules/Services.jsm");
 const {console} = Cu.import("resource://gre/modules/devtools/Console.jsm", {});
-const {Promise: promise} = Cu.import("resource://gre/modules/Promise.jsm", {});
 const {devtools: {require}} = Cu.import("resource://gre/modules/devtools/Loader.jsm", {});
 const {DebuggerClient} = Cu.import("resource://gre/modules/devtools/dbg-client.jsm", {});
 const {DebuggerServer} = Cu.import("resource://gre/modules/devtools/dbg-server.jsm", {});
 
 const PATH = "browser/toolkit/devtools/server/tests/browser/";
 const MAIN_DOMAIN = "http://test1.example.org/" + PATH;
 const ALT_DOMAIN = "http://sectest1.example.org/" + PATH;
 const ALT_DOMAIN_SECURED = "https://sectest1.example.org:443/" + PATH;
@@ -38,21 +37,20 @@ let addTab = Task.async(function* (url) 
   let tab = gBrowser.selectedTab = gBrowser.addTab();
   let loaded = once(gBrowser.selectedBrowser, "load", true);
 
   content.location = url;
   yield loaded;
 
   info("URL '" + url + "' loading complete");
 
-  let def = promise.defer();
-  let isBlank = url == "about:blank";
-  waitForFocus(def.resolve, content, isBlank);
-
-  yield def.promise;
+  yield new Promise(resolve => {
+    let isBlank = url == "about:blank";
+    waitForFocus(resolve, content, isBlank);
+  });;
 
   return tab.linkedBrowser.contentWindow.document;
 });
 
 function initDebuggerServer() {
   try {
     // Sometimes debugger server does not get destroyed correctly by previous
     // tests.
@@ -64,65 +62,62 @@ function initDebuggerServer() {
 
 /**
  * Connect a debugger client.
  * @param {DebuggerClient}
  * @return {Promise} Resolves to the selected tabActor form when the client is
  * connected.
  */
 function connectDebuggerClient(client) {
-  let def = promise.defer();
-  client.connect(() => {
-    client.listTabs(tabs => {
-      def.resolve(tabs.tabs[tabs.selected]);
+  return new Promise(resolve => {
+    client.connect(() => {
+      client.listTabs(tabs => {
+        resolve(tabs.tabs[tabs.selected]);
+      });
     });
   });
-  return def.promise;
 }
 
 /**
  * Close a debugger client's connection.
  * @param {DebuggerClient}
  * @return {Promise} Resolves when the connection is closed.
  */
 function closeDebuggerClient(client) {
-  let def = promise.defer();
-  client.close(def.resolve);
-  return def.promise;
+  return new Promise(resolve => client.close(resolve));
 }
 
 /**
  * Wait for eventName on target.
  * @param {Object} target An observable object that either supports on/off or
  * addEventListener/removeEventListener
  * @param {String} eventName
  * @param {Boolean} useCapture Optional, for addEventListener/removeEventListener
  * @return A promise that resolves when the event has been handled
  */
 function once(target, eventName, useCapture=false) {
   info("Waiting for event: '" + eventName + "' on " + target + ".");
 
-  let deferred = promise.defer();
+  return new Promise(resolve => {
 
-  for (let [add, remove] of [
-    ["addEventListener", "removeEventListener"],
-    ["addListener", "removeListener"],
-    ["on", "off"]
-  ]) {
-    if ((add in target) && (remove in target)) {
-      target[add](eventName, function onEvent(...aArgs) {
-        info("Got event: '" + eventName + "' on " + target + ".");
-        target[remove](eventName, onEvent, useCapture);
-        deferred.resolve.apply(deferred, aArgs);
-      }, useCapture);
-      break;
+    for (let [add, remove] of [
+      ["addEventListener", "removeEventListener"],
+      ["addListener", "removeListener"],
+      ["on", "off"]
+    ]) {
+      if ((add in target) && (remove in target)) {
+        target[add](eventName, function onEvent(...aArgs) {
+          info("Got event: '" + eventName + "' on " + target + ".");
+          target[remove](eventName, onEvent, useCapture);
+          resolve(...aArgs);
+        }, useCapture);
+        break;
+      }
     }
-  }
-
-  return deferred.promise;
+  });
 }
 
 /**
  * Forces GC, CC and Shrinking GC to get rid of disconnected docshells and
  * windows.
  */
 function forceCollections() {
   Cu.forceGC();