--- a/devtools/client/webaudioeditor/includes.js
+++ b/devtools/client/webaudioeditor/includes.js
@@ -1,17 +1,16 @@
 /* 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 { loader, require } = ChromeUtils.import("resource://devtools/shared/Loader.jsm", {});
 const { XPCOMUtils } = require("resource://gre/modules/XPCOMUtils.jsm");
 const { Task } = require("devtools/shared/task");
-const OldEventEmitter = require("devtools/shared/old-event-emitter");
 const EventEmitter = require("devtools/shared/event-emitter");
 const DevToolsUtils = require("devtools/shared/DevToolsUtils");
 const Services = require("Services");
 const { gDevTools } = require("devtools/client/framework/devtools");
 const { LocalizationHelper } = require("devtools/shared/l10n");
 const { ViewHelpers } = require("devtools/client/shared/widgets/view-helpers");
 
 // Use privileged promise in panel documents to prevent having them to freeze
@@ -76,17 +75,17 @@ XPCOMUtils.defineConstant(this, "EVENTS"
 /**
  * The current target and the Web Audio Editor front, set by this tool's host.
  */
 var gToolbox, gTarget, gFront;
 
 /**
  * Convenient way of emitting events from the panel window.
  */
-OldEventEmitter.decorate(this);
+EventEmitter.decorate(this);
 
 /**
  * DOM query helper.
  */
 function $(selector, target = document) { return target.querySelector(selector); }
 function $$(selector, target = document) { return target.querySelectorAll(selector); }
 
 /**

--- a/devtools/client/webaudioeditor/panel.js
+++ b/devtools/client/webaudioeditor/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 { Cc, Ci, Cu, Cr } = require("chrome");
-const EventEmitter = require("devtools/shared/old-event-emitter");
+const EventEmitter = require("devtools/shared/event-emitter");
 const { WebAudioFront } = require("devtools/shared/fronts/webaudio");
 
 function WebAudioEditorPanel(iframeWindow, toolbox) {
   this.panelWin = iframeWindow;
   this._toolbox = toolbox;
   this._destroyer = null;
 
   EventEmitter.decorate(this);

--- a/devtools/client/webaudioeditor/test/head.js
+++ b/devtools/client/webaudioeditor/test/head.js
@@ -146,17 +146,17 @@ function getNSpread(front, eventName, co
  * resolves when the graph was rendered with the correct count of
  * nodes and edges.
  */
 function waitForGraphRendered(front, nodeCount, edgeCount, paramEdgeCount) {
   let eventName = front.EVENTS.UI_GRAPH_RENDERED;
   info(`Wait for graph rendered with ${nodeCount} nodes, ${edgeCount} edges`);
 
   return new Promise((resolve, reject) => {
-    front.on(eventName, function onGraphRendered(_, nodes, edges, pEdges) {
+    front.on(eventName, function onGraphRendered(nodes, edges, pEdges) {
       let paramEdgesDone = paramEdgeCount != null ? paramEdgeCount === pEdges : true;
       info(`Got graph rendered with ${nodes} / ${nodeCount} nodes, ` +
            `${edges} / ${edgeCount} edges`);
       if (nodes === nodeCount && edges === edgeCount && paramEdgesDone) {
         front.off(eventName, onGraphRendered);
         resolve();
       }
     });
@@ -202,42 +202,42 @@ function checkVariableView(view, index, 
 }
 
 function modifyVariableView(win, view, index, prop, value) {
   let scope = view.getScopeAtIndex(index);
   let aVar = scope.get(prop);
   scope.expand();
 
   return new Promise((resolve, reject) => {
-    win.on(win.EVENTS.UI_SET_PARAM, handleSetting);
-    win.on(win.EVENTS.UI_SET_PARAM_ERROR, handleSetting);
+    const onParamSetSuccess = () => {
+      win.off(win.EVENTS.UI_SET_PARAM_ERROR, onParamSetError);
+      resolve();
+    }
+
+    const onParamSetError = () => {
+      win.off(win.EVENTS.UI_SET_PARAM, onParamSetSuccess);
+      reject();
+    }
+    win.once(win.EVENTS.UI_SET_PARAM, onParamSetSuccess);
+    win.once(win.EVENTS.UI_SET_PARAM_ERROR, onParamSetError);
 
     // Focus and select the variable to begin editing
     win.focus();
     aVar.focus();
     EventUtils.sendKey("RETURN", win);
 
     // Must wait for the scope DOM to be available to receive
     // events
     executeSoon(() => {
       info("Setting " + value + " for " + prop + "....");
       for (let c of (value + "")) {
         EventUtils.synthesizeKey(c, {}, win);
       }
       EventUtils.sendKey("RETURN", win);
     });
-
-    function handleSetting(eventName) {
-      win.off(win.EVENTS.UI_SET_PARAM, handleSetting);
-      win.off(win.EVENTS.UI_SET_PARAM_ERROR, handleSetting);
-      if (eventName === win.EVENTS.UI_SET_PARAM)
-        resolve();
-      if (eventName === win.EVENTS.UI_SET_PARAM_ERROR)
-        reject();
-    }
   });
 }
 
 function findGraphEdge(win, source, target, param) {
   let selector = ".edgePaths .edgePath[data-source='" + source + "'][data-target='" + target + "']";
   if (param) {
     selector += "[data-param='" + param + "']";
   }

--- a/devtools/client/webaudioeditor/views/automation.js
+++ b/devtools/client/webaudioeditor/views/automation.js
@@ -148,12 +148,12 @@ var AutomationView = {
    */
   _onResize: function () {
     this.graph.refresh();
   },
 
   /**
    * Called when the inspector view determines a node is selected.
    */
-  _onNodeSet: function (_, id) {
+  _onNodeSet: function (id) {
     this._setAudioNode(id != null ? gAudioNodes.get(id) : null);
   }
 };

--- a/devtools/client/webaudioeditor/views/context.js
+++ b/devtools/client/webaudioeditor/views/context.js
@@ -280,17 +280,17 @@ var ContextView = {
     if (~GRAPH_REDRAW_EVENTS.indexOf(eventName)) {
       this.draw();
     }
   },
 
   /**
    * Fired when the devtools theme changes.
    */
-  _onThemeChange: function (eventName, theme) {
+  _onThemeChange: function (theme) {
     let markerColor = MARKER_STYLING[theme];
     let marker = $("#arrowhead");
     if (marker) {
       marker.setAttribute("style", "fill: " + markerColor);
     }
   },
 
   /**

--- a/devtools/client/webaudioeditor/views/inspector.js
+++ b/devtools/client/webaudioeditor/views/inspector.js
@@ -136,17 +136,17 @@ var InspectorView = {
   /**
    * Event handlers
    */
 
   /**
    * Called on EVENTS.UI_SELECT_NODE, and takes an actorID `id`
    * and calls `setCurrentAudioNode` to scaffold the inspector view.
    */
-  _onNodeSelect: function (_, id) {
+  _onNodeSelect: function (id) {
     this.setCurrentAudioNode(gAudioNodes.get(id));
 
     // Ensure inspector is visible when selecting a new node
     this.show();
   },
 
   _onResize: function () {
     if (this.el.getAttribute("width") < MIN_INSPECTOR_WIDTH) {

--- a/devtools/client/webaudioeditor/views/properties.js
+++ b/devtools/client/webaudioeditor/views/properties.js
@@ -114,17 +114,17 @@ var PropertiesView = {
 
   /**
    * Event handlers
    */
 
   /**
    * Called when the inspector view determines a node is selected.
    */
-  _onNodeSet: function (_, id) {
+  _onNodeSet: function (id) {
     this._setAudioNode(gAudioNodes.get(id));
   },
 
   /**
    * Executed when an audio prop is changed in the UI.
    */
   _onEval: Task.async(function* (variable, value) {
     let ownerScope = variable.ownerView;