--- a/devtools/client/framework/sidebar.js
+++ b/devtools/client/framework/sidebar.js
@@ -1,17 +1,17 @@
 /* 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";
 
 var Services = require("Services");
 var {Task} = require("devtools/shared/task");
-var EventEmitter = require("devtools/shared/old-event-emitter");
+var EventEmitter = require("devtools/shared/event-emitter");
 var Telemetry = require("devtools/client/shared/telemetry");
 
 const {LocalizationHelper} = require("devtools/shared/l10n");
 const L10N = new LocalizationHelper("devtools/client/locales/toolbox.properties");
 
 const XULNS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
 
 /**

--- a/devtools/client/framework/test/browser_toolbox_sidebar.js
+++ b/devtools/client/framework/test/browser_toolbox_sidebar.js
@@ -43,40 +43,40 @@ function test() {
     gDevTools.showToolbox(target, toolDefinition.id).then(function (toolbox) {
       let panel = toolbox.getPanel(toolDefinition.id);
       panel.toolbox = toolbox;
       ok(true, "Tool open");
 
       let tabbox = panel.panelDoc.getElementById("sidebar");
       panel.sidebar = new ToolSidebar(tabbox, panel, "testbug865688", true);
 
-      panel.sidebar.on("new-tab-registered", function (event, id) {
+      panel.sidebar.on("new-tab-registered", function (id) {
         registeredTabs[id] = true;
       });
 
-      panel.sidebar.once("tab1-ready", function (event) {
-        info(event);
+      panel.sidebar.once("tab1-ready", function () {
+        info("tab1-ready");
         readyTabs.tab1 = true;
         allTabsReady(panel);
       });
 
-      panel.sidebar.once("tab2-ready", function (event) {
-        info(event);
+      panel.sidebar.once("tab2-ready", function () {
+        info("tab2-ready");
         readyTabs.tab2 = true;
         allTabsReady(panel);
       });
 
-      panel.sidebar.once("tab3-ready", function (event) {
-        info(event);
+      panel.sidebar.once("tab3-ready", function () {
+        info("tab3-ready");
         readyTabs.tab3 = true;
         allTabsReady(panel);
       });
 
-      panel.sidebar.once("tab1-selected", function (event) {
-        info(event);
+      panel.sidebar.once("tab1-selected", function () {
+        info("tab1-selected");
         tab1Selected = true;
         allTabsReady(panel);
       });
 
       panel.sidebar.addTab("tab1", tab1URL, {selected: true});
       panel.sidebar.addTab("tab2", tab2URL);
       panel.sidebar.addTab("tab3", tab3URL);
 
@@ -122,18 +122,18 @@ function test() {
         testRemoval(panel);
       });
     });
 
     panel.sidebar.select("tab2");
   }
 
   function testRemoval(panel) {
-    panel.sidebar.once("tab-unregistered", function (event, id) {
-      info(event);
+    panel.sidebar.once("tab-unregistered", function (id) {
+      info("tab-unregistered");
       registeredTabs[id] = false;
 
       is(id, "tab3", "The right tab must be removed");
 
       let tabs = panel.sidebar._tabbox.querySelectorAll("tab");
       let panels = panel.sidebar._tabbox.querySelectorAll("tabpanel");
 
       is(tabs.length, 2, "There is the right number of tabs");

--- a/devtools/client/framework/test/browser_toolbox_sidebar_events.js
+++ b/devtools/client/framework/test/browser_toolbox_sidebar_events.js
@@ -34,33 +34,33 @@ function test() {
   gDevTools.registerTool(toolDefinition);
 
   addTab("about:blank").then(function (aTab) {
     let target = TargetFactory.forTab(aTab);
     gDevTools.showToolbox(target, toolDefinition.id).then(function (toolbox) {
       let panel = toolbox.getPanel(toolDefinition.id);
       ok(true, "Tool open");
 
-      panel.once("sidebar-created", function (event, id) {
-        collectedEvents.push(event);
+      panel.once("sidebar-created", function () {
+        collectedEvents.push("sidebar-created");
       });
 
-      panel.once("sidebar-destroyed", function (event, id) {
-        collectedEvents.push(event);
+      panel.once("sidebar-destroyed", function () {
+        collectedEvents.push("sidebar-destroyed");
       });
 
       let tabbox = panel.panelDoc.getElementById("sidebar");
       panel.sidebar = new ToolSidebar(tabbox, panel, "testbug1072208", true);
 
-      panel.sidebar.once("show", function (event, id) {
-        collectedEvents.push(event);
+      panel.sidebar.once("show", function () {
+        collectedEvents.push("show");
       });
 
-      panel.sidebar.once("hide", function (event, id) {
-        collectedEvents.push(event);
+      panel.sidebar.once("hide", function () {
+        collectedEvents.push("hide");
       });
 
       panel.sidebar.once("tab1-selected", () => finishUp(panel));
       panel.sidebar.addTab("tab1", tab1URL, {selected: true});
       panel.sidebar.show();
     }).catch(console.error);
   });
 

--- a/devtools/client/scratchpad/scratchpad-panel.js
+++ b/devtools/client/scratchpad/scratchpad-panel.js
@@ -1,17 +1,17 @@
 /* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
 /* vim: set ft=javascript ts=2 et sw=2 tw=80: */
 /* 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";
 
 const {Cu} = require("chrome");
-const EventEmitter = require("devtools/shared/old-event-emitter");
+const EventEmitter = require("devtools/shared/event-emitter");
 const promise = require("promise");
 const defer = require("devtools/shared/defer");
 
 
 function ScratchpadPanel(iframeWindow, toolbox) {
   let { Scratchpad } = iframeWindow;
   this._toolbox = toolbox;
   this.panelWin = iframeWindow;

--- a/devtools/client/scratchpad/scratchpad.js
+++ b/devtools/client/scratchpad/scratchpad.js
@@ -38,17 +38,17 @@ const TAB_SIZE = "devtools.editor.tabsiz
 const FALLBACK_CHARSET_LIST = "intl.fallbackCharsetList.ISO-8859-1";
 
 const VARIABLES_VIEW_URL = "chrome://devtools/content/shared/widgets/VariablesView.xul";
 
 const {require, loader} = ChromeUtils.import("resource://devtools/shared/Loader.jsm", {});
 
 const Editor = require("devtools/client/sourceeditor/editor");
 const TargetFactory = require("devtools/client/framework/target").TargetFactory;
-const EventEmitter = require("devtools/shared/old-event-emitter");
+const EventEmitter = require("devtools/shared/event-emitter");
 const {DevToolsWorker} = require("devtools/shared/worker/worker");
 const DevToolsUtils = require("devtools/shared/DevToolsUtils");
 const flags = require("devtools/shared/flags");
 const promise = require("promise");
 const defer = require("devtools/shared/defer");
 const Services = require("Services");
 const {gDevTools} = require("devtools/client/framework/devtools");
 const { extend } = require("devtools/shared/extend");