--- a/devtools/client/inspector/shared/test/head.js
+++ b/devtools/client/inspector/shared/test/head.js
@@ -34,17 +34,17 @@ registerCleanupFunction(() => {
  * (the instance of the current toolbox, or inspector panel for instance).
  *
  * Most of these functions are async too and return promises.
  *
  * All tests should follow the following pattern:
  *
  * add_task(function*() {
  *   yield addTab(TEST_URI);
- *   let {toolbox, inspector, view} = yield openInspector();
+ *   let {toolbox, inspector} = yield openInspector();
  *   inspector.sidebar.select(viewId);
  *   let view = inspector[viewId].view;
  *   yield selectNode("#test", inspector);
  *   yield someAsyncTestFunction(view);
  * });
  *
  * add_task is the way to define the testcase in the test file. It accepts
  * a single generator-function argument.

--- a/devtools/client/styleeditor/test/browser_styleeditor_filesave.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_filesave.js
@@ -3,19 +3,16 @@
    http://creativecommons.org/publicdomain/zero/1.0/ */
 "use strict";
 
 // Test that 'Save' function works.
 
 const TESTCASE_URI_HTML = TEST_BASE_HTTP + "simple.html";
 const TESTCASE_URI_CSS = TEST_BASE_HTTP + "simple.css";
 
-var Cc = Components.classes;
-var Ci = Components.interfaces;
-
 var tempScope = {};
 Components.utils.import("resource://gre/modules/FileUtils.jsm", tempScope);
 Components.utils.import("resource://gre/modules/NetUtil.jsm", tempScope);
 var FileUtils = tempScope.FileUtils;
 var NetUtil = tempScope.NetUtil;
 
 add_task(function* () {
   let htmlFile = yield copy(TESTCASE_URI_HTML, "simple.html");

--- a/devtools/client/styleeditor/test/browser_styleeditor_media_sidebar_links.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_media_sidebar_links.js
@@ -41,17 +41,17 @@ function testNumberOfLinks(editor) {
   is(conditions[3].querySelectorAll(responsiveModeToggleClass).length, 2,
        "There should be 2 responsive mode links in the media rule");
 }
 
 function* testMediaLink(editor, tab, ui, itemIndex, type, value) {
   let sidebar = editor.details.querySelector(".stylesheet-sidebar");
   let conditions = sidebar.querySelectorAll(".media-rule-condition");
 
-  let onMediaChange = once("media-list-changed", ui);
+  let onMediaChange = once(ui, "media-list-changed");
   let onContentResize = waitForResizeTo(ResponsiveUIManager, type, value);
 
   info("Launching responsive mode");
   conditions[itemIndex].querySelector(responsiveModeToggleClass).click();
 
   ResponsiveUIManager.getResponsiveUIForTab(tab).transitionsEnabled = false;
 
   info("Waiting for the @media list to update");
@@ -66,18 +66,18 @@ function* testMediaLink(editor, tab, ui,
 
   let dimension = (yield getSizing())[type];
   is(dimension, value, `${type} should be properly set.`);
 }
 
 function* closeRDM(tab, ui) {
   info("Closing responsive mode");
   ResponsiveUIManager.toggle(window, tab);
-  let onMediaChange = once("media-list-changed", ui);
-  yield once("off", ResponsiveUIManager);
+  let onMediaChange = once(ui, "media-list-changed");
+  yield once(ResponsiveUIManager, "off");
   yield onMediaChange;
   ok(!ResponsiveUIManager.isActiveForTab(tab),
      "Responsive mode should no longer be active.");
 }
 
 function doFinalChecks(editor) {
   let sidebar = editor.details.querySelector(".stylesheet-sidebar");
   let conditions = sidebar.querySelectorAll(".media-rule-condition");
@@ -110,24 +110,16 @@ function* getSizing() {
     return {
       width: content.innerWidth,
       height: content.innerHeight
     };
   });
   return sizing;
 }
 
-function once(event, target) {
-  let deferred = promise.defer();
-  target.once(event, () => {
-    deferred.resolve();
-  });
-  return deferred.promise;
-}
-
 function openEditor(editor) {
   getLinkFor(editor).click();
 
   return editor.getSourceEditor();
 }
 
 function getLinkFor(editor) {
   return editor.summary.querySelector(".stylesheet-name");

--- a/devtools/client/styleeditor/test/browser_styleeditor_sourcemap_watching.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_sourcemap_watching.js
@@ -10,19 +10,16 @@ const TESTCASE_URI_REG_CSS = TEST_BASE_H
 const TESTCASE_URI_SCSS = TEST_BASE_HTTP + "sourcemap-sass/sourcemaps.scss";
 const TESTCASE_URI_MAP = TEST_BASE_HTTP + "sourcemap-css/sourcemaps.css.map";
 const TESTCASE_SCSS_NAME = "sourcemaps.scss";
 
 const TRANSITIONS_PREF = "devtools.styleeditor.transitions";
 
 const CSS_TEXT = "* { color: blue }";
 
-const Cc = Components.classes;
-const Ci = Components.interfaces;
-
 const {FileUtils} = Components.utils.import("resource://gre/modules/FileUtils.jsm", {});
 const {NetUtil} = Components.utils.import("resource://gre/modules/NetUtil.jsm", {});
 
 add_task(function* () {
   yield new Promise(resolve => {
     SpecialPowers.pushPrefEnv({"set": [
       [TRANSITIONS_PREF, false]
     ]}, resolve);

--- a/devtools/client/styleeditor/test/browser_styleeditor_sync.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_sync.js
@@ -1,19 +1,16 @@
 /* vim: set ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 "use strict";
 
 // Test that changes in the style inspector are synchronized into the
 // style editor.
 
-/* import-globals-from ../../inspector/shared/test/head.js */
-Services.scriptloader.loadSubScript("chrome://mochitests/content/browser/devtools/client/inspector/shared/test/head.js", this);
-
 const TESTCASE_URI = TEST_BASE_HTTP + "sync.html";
 
 const expectedText = `
   body {
     border-width: 15px;
     /*! color: red; */
   }
 

--- a/devtools/client/styleeditor/test/browser_styleeditor_syncAddRule.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_syncAddRule.js
@@ -1,18 +1,15 @@
 /* vim: set ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 "use strict";
 
 // Test that adding a new rule is synced to the style editor.
 
-/* import-globals-from ../../inspector/shared/test/head.js */
-Services.scriptloader.loadSubScript("chrome://mochitests/content/browser/devtools/client/inspector/shared/test/head.js", this);
-
 const TESTCASE_URI = TEST_BASE_HTTP + "sync.html";
 
 const expectedText = `
 #testid {
 }`;
 
 add_task(function* () {
   yield addTab(TESTCASE_URI);

--- a/devtools/client/styleeditor/test/browser_styleeditor_syncAlreadyOpen.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_syncAlreadyOpen.js
@@ -1,46 +1,43 @@
 /* vim: set ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 "use strict";
 
 // Test that changes in the style inspector are synchronized into the
 // style editor.
 
-/* import-globals-from ../../inspector/shared/test/head.js */
-Services.scriptloader.loadSubScript("chrome://mochitests/content/browser/devtools/client/inspector/shared/test/head.js", this);
-
 const TESTCASE_URI = TEST_BASE_HTTP + "sync.html";
 
 const expectedText = `
   body {
     border-width: 15px;
     color: red;
   }
 
   #testid {
     /*! font-size: 4em; */
   }
   `;
 
 add_task(function* () {
   yield addTab(TESTCASE_URI);
 
-  let { inspector, view } = yield openRuleView();
+  let { inspector, view, toolbox } = yield openRuleView();
 
   // In this test, make sure the style editor is open before making
   // changes in the inspector.
   let { ui } = yield openStyleEditor();
   let editor = yield ui.editors[0].getSourceEditor();
 
   let onEditorChange = promise.defer();
   editor.sourceEditor.on("change", onEditorChange.resolve);
 
-  yield openRuleView();
+  yield toolbox.getPanel("inspector");
   yield selectNode("#testid", inspector);
   let ruleEditor = getRuleViewRuleEditor(view, 1);
 
   // Disable the "font-size" property.
   let propEditor = ruleEditor.rule.textProps[0].editor;
   let onModification = view.once("ruleview-changed");
   propEditor.enable.click();
   yield onModification;

--- a/devtools/client/styleeditor/test/browser_styleeditor_syncEditSelector.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_syncEditSelector.js
@@ -1,19 +1,16 @@
 /* vim: set ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 "use strict";
 
 // Test that changes in the style inspector are synchronized into the
 // style editor.
 
-/* import-globals-from ../../inspector/shared/test/head.js */
-Services.scriptloader.loadSubScript("chrome://mochitests/content/browser/devtools/client/inspector/shared/test/head.js", this);
-
 const TESTCASE_URI = TEST_BASE_HTTP + "sync.html";
 
 const expectedText = `
   body {
     border-width: 15px;
     color: red;
   }
 

--- a/devtools/client/styleeditor/test/browser_styleeditor_syncIntoRuleView.js
+++ b/devtools/client/styleeditor/test/browser_styleeditor_syncIntoRuleView.js
@@ -1,19 +1,16 @@
 /* vim: set ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 "use strict";
 
 // Test that changes in the style editor are synchronized into the
 // style inspector.
 
-/* import-globals-from ../../inspector/shared/test/head.js */
-Services.scriptloader.loadSubScript("chrome://mochitests/content/browser/devtools/client/inspector/shared/test/head.js", this);
-
 const TEST_URI = `
   <style type='text/css'>
     div { background-color: seagreen; }
   </style>
   <div id='testid' class='testclass'>Styled Node</div>
 `;
 
 const TESTCASE_CSS_SOURCE = "#testid { color: chartreuse; }";

--- a/devtools/client/styleeditor/test/head.js
+++ b/devtools/client/styleeditor/test/head.js
@@ -1,53 +1,47 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
 /* All top-level definitions here are exports.  */
 /* eslint no-unused-vars: [2, {"vars": "local"}] */
 
 "use strict";
 
+/* import-globals-from ../../inspector/shared/test/head.js */
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/devtools/client/inspector/shared/test/head.js", this);
+
 const TEST_BASE = "chrome://mochitests/content/browser/devtools/client/styleeditor/test/";
 const TEST_BASE_HTTP = "http://example.com/browser/devtools/client/styleeditor/test/";
 const TEST_BASE_HTTPS = "https://example.com/browser/devtools/client/styleeditor/test/";
 const TEST_HOST = "mochi.test:8888";
 
-var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-var {TargetFactory} = require("devtools/client/framework/target");
-var promise = require("promise");
-var DevToolsUtils = require("devtools/shared/DevToolsUtils");
-
-DevToolsUtils.testing = true;
-SimpleTest.registerCleanupFunction(() => {
-  DevToolsUtils.testing = false;
-});
-
 /**
  * Add a new test tab in the browser and load the given url.
  * @param {String} url The url to be loaded in the new tab
  * @param {Window} win The window to add the tab to (default: current window).
  * @return a promise that resolves to the tab object when the url is loaded
  */
-function addTab(url, win) {
+var addTab = function(url, win) {
   info("Adding a new tab with URL: '" + url + "'");
   let def = promise.defer();
 
   let targetWindow = win || window;
   let targetBrowser = targetWindow.gBrowser;
 
   let tab = targetBrowser.selectedTab = targetBrowser.addTab(url);
   targetBrowser.selectedBrowser.addEventListener("load", function onload() {
     targetBrowser.selectedBrowser.removeEventListener("load", onload, true);
     info("URL '" + url + "' loading complete");
     def.resolve(tab);
   }, true);
 
   return def.promise;
-}
+};
 
 /**
  * Navigate the currently selected tab to a new URL and wait for it to load.
  * @param {String} url The url to be loaded in the current tab.
  * @return a promise that resolves when the page has fully loaded.
  */
 var navigateTo = Task.async(function* (url) {
   info(`Navigating to ${url}`);
@@ -74,25 +68,16 @@ var reloadPageAndWaitForStyleSheets = Ta
   info("Reloading the page.");
 
   let onReset = ui.once("stylesheets-reset");
   let browser = gBrowser.selectedBrowser;
   yield ContentTask.spawn(browser, null, "() => content.location.reload()");
   yield onReset;
 });
 
-registerCleanupFunction(function* () {
-  while (gBrowser.tabs.length > 1) {
-    let target = TargetFactory.forTab(gBrowser.selectedTab);
-    yield gDevTools.closeToolbox(target);
-
-    gBrowser.removeCurrentTab();
-  }
-});
-
 /**
  * Open the style editor for the current tab.
  */
 var openStyleEditor = Task.async(function* (tab) {
   if (!tab) {
     tab = gBrowser.selectedTab;
   }
   let target = TargetFactory.forTab(tab);
@@ -120,17 +105,17 @@ var openStyleEditorForURL = Task.async(f
  *
  * @param {String} selector
  *        The selector used to obtain the element.
  * @param {String} pseudo
  *        pseudo id to query, or null.
  * @param {String} name
  *        name of the property.
  */
-function* getComputedStyleProperty(args) {
+var getComputedStyleProperty = function* (args) {
   return yield ContentTask.spawn(gBrowser.selectedBrowser, args,
     function({selector, pseudo, name}) {
       let element = content.document.querySelector(selector);
       let style = content.getComputedStyle(element, pseudo);
       return style.getPropertyValue(name);
     }
   );
-}
+};