From 7b53fcdbb6bf4549c9fcc317cc9e942a05129348 Mon Sep 17 00:00:00 2001
From: Fabien Casters <fabien@vaga.io>
Date: Mon, 13 Mar 2017 21:15:44 +0100
Subject: [PATCH] Bug 1325988 - Fix ESLint issues in
 devtools/server/tests/mochitest/ r=tromey

MozReview-Commit-ID: BFaOv5i5Tun

--HG--
extra : rebase_source : 5c2b5d1867eb5b48c56725b87d71dae72a83eb34
---
 .eslintignore                                 |   1 -
 .../Debugger.Source.prototype.element-2.js    |   3 +
 .../Debugger.Source.prototype.element.html    |  10 +-
 .../Debugger.Source.prototype.element.js      |   7 +-
 .../tests/mochitest/animation-data.html       |   6 +-
 .../tests/mochitest/director-helpers.js       |  12 +-
 .../server/tests/mochitest/hello-actor.js     |   2 +
 .../tests/mochitest/inspector-eyedropper.html |  38 ++--
 .../tests/mochitest/inspector-helpers.js      |  43 ++--
 .../mochitest/inspector-search-data.html      |   8 +-
 .../mochitest/inspector-styles-data.html      |   6 +-
 .../mochitest/inspector-traversal-data.html   |  21 +-
 .../mochitest/inspector_css-properties.html   |   6 +-
 .../mochitest/inspector_getImageData.html     |   6 +-
 .../server/tests/mochitest/memory-helpers.js  |  27 +--
 .../nonchrome_unsafeDereference.html          |   6 +-
 .../server/tests/mochitest/setup-in-child.js  |   6 +-
 .../server/tests/mochitest/setup-in-parent.js |   2 +
 ...test_Debugger.Script.prototype.global.html |  14 +-
 ...est_Debugger.Source.prototype.element.html |  86 ++++----
 ...r.Source.prototype.introductionScript.html |  23 +-
 ...ger.Source.prototype.introductionType.html |  63 +++---
 .../test_animation_actor-lifetime.html        |  27 ++-
 .../tests/mochitest/test_connectToChild.html  |  23 +-
 .../mochitest/test_connection-manager.html    |  95 +++++----
 .../test_css-logic-media-queries.html         |  12 +-
 .../mochitest/test_css-logic-specificity.html |  12 +-
 .../tests/mochitest/test_css-logic.html       |  42 ++--
 .../tests/mochitest/test_css-properties.html  |  24 ++-
 .../server/tests/mochitest/test_device.html   |  61 +++---
 .../server/tests/mochitest/test_director.html |  38 ++--
 .../test_director_connectToChild.html         |  31 ++-
 .../test_executeInGlobal-outerized_this.html  |  38 ++--
 .../tests/mochitest/test_framerate_01.html    |  73 +++----
 .../tests/mochitest/test_framerate_02.html    |  52 ++---
 .../tests/mochitest/test_framerate_03.html    |  41 ++--
 .../tests/mochitest/test_framerate_04.html    |  27 +--
 .../tests/mochitest/test_framerate_05.html    |  33 +--
 .../tests/mochitest/test_framerate_06.html    |  41 ++--
 .../tests/mochitest/test_getProcess.html      |  25 ++-
 .../mochitest/test_inspector-anonymous.html   | 118 ++++++-----
 .../mochitest/test_inspector-changeattrs.html |  41 ++--
 .../mochitest/test_inspector-changevalue.html |  28 +--
 .../mochitest/test_inspector-dead-nodes.html  |  60 +++---
 .../test_inspector-duplicate-node.html        |  22 +-
 .../tests/mochitest/test_inspector-hide.html  |  17 +-
 .../mochitest/test_inspector-insert.html      |  31 ++-
 .../test_inspector-mutations-attr.html        |  65 +++---
 .../test_inspector-mutations-childlist.html   |  82 ++++---
 .../test_inspector-mutations-events.html      |  57 +++--
 .../test_inspector-mutations-frameload.html   |  31 ++-
 .../test_inspector-mutations-value.html       |  32 ++-
 .../mochitest/test_inspector-pick-color.html  | 200 +++++++++---------
 .../test_inspector-pseudoclass-lock.html      |  81 +++----
 .../mochitest/test_inspector-release.html     |  24 +--
 .../mochitest/test_inspector-reload.html      |  22 +-
 .../mochitest/test_inspector-remove.html      |  26 +--
 .../mochitest/test_inspector-resize.html      |  13 +-
 .../mochitest/test_inspector-resolve-url.html |  43 ++--
 .../mochitest/test_inspector-retain.html      |  47 ++--
 .../test_inspector-scroll-into-view.html      |  23 +-
 .../test_inspector-search-front.html          |  21 +-
 .../mochitest/test_inspector-search.html      |  27 ++-
 .../mochitest/test_inspector-traversal.html   |  86 ++++----
 ..._inspector_getImageData-wait-for-load.html |  24 ++-
 .../test_inspector_getImageData.html          |  16 +-
 .../test_inspector_getImageDataFromURL.html   |  15 +-
 .../test_inspector_getNodeFromActor.html      |  32 +--
 .../test_makeGlobalObjectReference.html       |  43 ++--
 .../server/tests/mochitest/test_memory.html   |   8 +-
 .../mochitest/test_memory_allocations_01.html |  34 +--
 .../mochitest/test_memory_allocations_02.html |  30 +--
 .../mochitest/test_memory_allocations_03.html |  16 +-
 .../mochitest/test_memory_allocations_04.html |  14 +-
 .../mochitest/test_memory_allocations_05.html |  38 ++--
 .../mochitest/test_memory_allocations_06.html |  12 +-
 .../mochitest/test_memory_allocations_07.html |  17 +-
 .../mochitest/test_memory_attach_01.html      |   8 +-
 .../mochitest/test_memory_attach_02.html      |  14 +-
 .../tests/mochitest/test_memory_census.html   |   8 +-
 .../tests/mochitest/test_memory_gc_01.html    |  22 +-
 .../mochitest/test_memory_gc_events.html      |  10 +-
 .../tests/mochitest/test_preference.html      |  63 +++---
 .../mochitest/test_setupInParentChild.html    |  12 +-
 .../tests/mochitest/test_styles-applied.html  |  40 ++--
 .../tests/mochitest/test_styles-computed.html | 145 +++++++------
 .../tests/mochitest/test_styles-layout.html   |  16 +-
 .../tests/mochitest/test_styles-matched.html  |  39 ++--
 .../tests/mochitest/test_styles-modify.html   |  18 +-
 .../tests/mochitest/test_styles-svg.html      |  19 +-
 .../mochitest/test_unsafeDereference.html     |  15 +-
 .../mochitest/test_websocket-server.html      |   6 +-
 92 files changed, 1568 insertions(+), 1454 deletions(-)

diff --git a/.eslintignore b/.eslintignore
index 6a1bfa5f1a8b..7c5d28696d4d 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -134,7 +134,6 @@ devtools/server/actors/stylesheets.js
 devtools/server/tests/browser/storage-*.html
 !devtools/server/tests/browser/storage-unsecured-iframe.html
 devtools/server/tests/browser/stylesheets-nested-iframes.html
-devtools/server/tests/mochitest/**
 devtools/server/tests/unit/**
 devtools/shared/platform/content/test/test_clipboard.html
 devtools/shared/qrcode/tests/mochitest/test_decode.html
diff --git a/devtools/server/tests/mochitest/Debugger.Source.prototype.element-2.js b/devtools/server/tests/mochitest/Debugger.Source.prototype.element-2.js
index eab74692130a..7260431428dc 100644
--- a/devtools/server/tests/mochitest/Debugger.Source.prototype.element-2.js
+++ b/devtools/server/tests/mochitest/Debugger.Source.prototype.element-2.js
@@ -1 +1,4 @@
+"use strict";
+
+// eslint-disable-next-line no-debugger
 debugger;
diff --git a/devtools/server/tests/mochitest/Debugger.Source.prototype.element.html b/devtools/server/tests/mochitest/Debugger.Source.prototype.element.html
index fcf4c6c851d5..6959ad970d1d 100644
--- a/devtools/server/tests/mochitest/Debugger.Source.prototype.element.html
+++ b/devtools/server/tests/mochitest/Debugger.Source.prototype.element.html
@@ -1,6 +1,14 @@
 <head>
   <!-- Static (not dynamically inserted) inline script. -->
-  <script id='franz'>function franz() { debugger; }</script>
+  <script id='franz'>
+  /* exported franz */
+  "use strict";
+
+  function franz() {
+    // eslint-disable-next-line no-debugger
+    debugger;
+  }
+  </script>
 
   <!-- Static out-of-line script element. -->
   <script id='heinrich' src='Debugger.Source.prototype.element.js'></script>
diff --git a/devtools/server/tests/mochitest/Debugger.Source.prototype.element.js b/devtools/server/tests/mochitest/Debugger.Source.prototype.element.js
index 44115b373be6..0fe4157a4401 100644
--- a/devtools/server/tests/mochitest/Debugger.Source.prototype.element.js
+++ b/devtools/server/tests/mochitest/Debugger.Source.prototype.element.js
@@ -1 +1,6 @@
-function heinrichFun() { franz(); }
+/* exported heinrichFun */
+"use strict";
+
+function heinrichFun() {
+  franz();
+}
diff --git a/devtools/server/tests/mochitest/animation-data.html b/devtools/server/tests/mochitest/animation-data.html
index 01be59548093..79bf3706c03d 100644
--- a/devtools/server/tests/mochitest/animation-data.html
+++ b/devtools/server/tests/mochitest/animation-data.html
@@ -101,8 +101,10 @@
     }
   </style>
   <script type="text/javascript">
-    window.onload = function() {
-      window.opener.postMessage('ready', '*');
+    "use strict";
+
+    window.onload = function () {
+      window.opener.postMessage("ready", "*");
     };
   </script>
 </head>
diff --git a/devtools/server/tests/mochitest/director-helpers.js b/devtools/server/tests/mochitest/director-helpers.js
index fe1f7d394a28..b650884a2853 100644
--- a/devtools/server/tests/mochitest/director-helpers.js
+++ b/devtools/server/tests/mochitest/director-helpers.js
@@ -1,4 +1,8 @@
-var Cu = Components.utils;
+/* exported DirectorRegistryFront, DirectorManagerFront, Task,
+   newConnectedDebuggerClient, purgeInstalledDirectorScripts */
+"use strict";
+
+const Cu = Components.utils;
 const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
 const {DebuggerClient} = require("devtools/shared/client/main");
 const {DebuggerServer} = require("devtools/server/main");
@@ -25,12 +29,12 @@ const { Task } = require("devtools/shared/task");
  **********************************/
 
 function* newConnectedDebuggerClient(opts) {
-  var transport = DebuggerServer.connectPipe();
-  var client = new DebuggerClient(transport);
+  let transport = DebuggerServer.connectPipe();
+  let client = new DebuggerClient(transport);
 
   yield client.connect();
 
-  var root = yield client.listTabs();
+  let root = yield client.listTabs();
 
   return {
     client: client,
diff --git a/devtools/server/tests/mochitest/hello-actor.js b/devtools/server/tests/mochitest/hello-actor.js
index 6031929381fb..abb6afc73fa8 100644
--- a/devtools/server/tests/mochitest/hello-actor.js
+++ b/devtools/server/tests/mochitest/hello-actor.js
@@ -1,5 +1,7 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
+/* exported HelloActor */
+"use strict";
 
 const protocol = require("devtools/shared/protocol");
 
diff --git a/devtools/server/tests/mochitest/inspector-eyedropper.html b/devtools/server/tests/mochitest/inspector-eyedropper.html
index ded9f392de2f..39705edcc220 100644
--- a/devtools/server/tests/mochitest/inspector-eyedropper.html
+++ b/devtools/server/tests/mochitest/inspector-eyedropper.html
@@ -1,18 +1,20 @@
-<html>
-<head>
-  <meta charset="UTF-8">
-  <title>Inspector Eyedropper tests</title>
-  <style>
-    html {
-      background: black;
-    }
-  </style>
-  <script type="text/javascript">
-    window.onload = function() {
-      window.opener.postMessage('ready', '*');
-    };
-  </script>
-</head>
-</body>
-</body>
-</html>
\ No newline at end of file
+<html>
+<head>
+  <meta charset="UTF-8">
+  <title>Inspector Eyedropper tests</title>
+  <style>
+    html {
+      background: black;
+    }
+  </style>
+  <script type="text/javascript">
+    "use strict";
+
+    window.onload = function () {
+      window.opener.postMessage("ready", "*");
+    };
+  </script>
+</head>
+</body>
+</body>
+</html>
diff --git a/devtools/server/tests/mochitest/inspector-helpers.js b/devtools/server/tests/mochitest/inspector-helpers.js
index 52c3fdc96646..d46c0ce88c5c 100644
--- a/devtools/server/tests/mochitest/inspector-helpers.js
+++ b/devtools/server/tests/mochitest/inspector-helpers.js
@@ -1,3 +1,9 @@
+/* exported attachURL, promiseDone, assertOwnershipTrees, checkMissing, checkAvailable,
+   promiseOnce, isSrcChange, isUnretained, isNewRoot, assertSrcChange, assertUnload,
+   assertFrameLoad, assertChildList, waitForMutation, addTest, addAsyncTest,
+   runNextTest */
+"use strict";
+
 var Cu = Components.utils;
 
 const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
@@ -15,7 +21,6 @@ SimpleTest.registerCleanupFunction(function () {
   Services.prefs.clearUserPref("devtools.debugger.log");
 });
 
-
 if (!DebuggerServer.initialized) {
   DebuggerServer.init();
   DebuggerServer.addBrowserActors();
@@ -40,8 +45,8 @@ SimpleTest.registerCleanupFunction(function () {
  * and disconnect its debugger client.
  */
 function attachURL(url, callback) {
-  var win = window.open(url, "_blank");
-  var client = null;
+  let win = window.open(url, "_blank");
+  let client = null;
 
   let cleanup = () => {
     if (client) {
@@ -63,7 +68,8 @@ function attachURL(url, callback) {
           for (let tab of response.tabs) {
             if (tab.url === url) {
               window.removeEventListener("message", loadListener);
-              client.attachTab(tab.actor, function (aResponse, aTabClient) {
+              // eslint-disable-next-line max-nested-callbacks
+              client.attachTab(tab.actor, function (_response, _tabClient) {
                 try {
                   callback(null, client, tab, win.document);
                 } catch (ex) {
@@ -125,15 +131,18 @@ function serverOwnershipTree(walker) {
 
   return {
     root: serverOwnershipSubtree(serverWalker, serverWalker.rootDoc),
-    orphaned: [...serverWalker._orphaned].map(o => serverOwnershipSubtree(serverWalker, o.rawNode)),
-    retained: [...serverWalker._retainedOrphans].map(o => serverOwnershipSubtree(serverWalker, o.rawNode))
+    orphaned: [...serverWalker._orphaned]
+              .map(o => serverOwnershipSubtree(serverWalker, o.rawNode)),
+    retained: [...serverWalker._retainedOrphans]
+              .map(o => serverOwnershipSubtree(serverWalker, o.rawNode))
   };
 }
 
 function clientOwnershipSubtree(node) {
   return {
     name: node.actorID,
-    children: sortOwnershipChildren(node.treeChildren().map(child => clientOwnershipSubtree(child)))
+    children: sortOwnershipChildren(node.treeChildren()
+              .map(child => clientOwnershipSubtree(child)))
   };
 }
 
@@ -156,7 +165,8 @@ function ownershipTreeSize(tree) {
 function assertOwnershipTrees(walker) {
   let serverTree = serverOwnershipTree(walker);
   let clientTree = clientOwnershipTree(walker);
-  is(JSON.stringify(clientTree, null, " "), JSON.stringify(serverTree, null, " "), "Server and client ownership trees should match.");
+  is(JSON.stringify(clientTree, null, " "), JSON.stringify(serverTree, null, " "),
+     "Server and client ownership trees should match.");
 
   return ownershipTreeSize(clientTree.root);
 }
@@ -189,14 +199,15 @@ function checkAvailable(client, actorID) {
     to: actorID,
     type: "garbageAvailableTest",
   }, response => {
-    is(response.error, "unrecognizedPacketType", "node list actor should be contactable.");
+    is(response.error, "unrecognizedPacketType",
+       "node list actor should be contactable.");
     deferred.resolve(undefined);
   });
   return deferred.promise;
 }
 
-function promiseDone(promise) {
-  promise.then(null, err => {
+function promiseDone(currentPromise) {
+  currentPromise.then(null, err => {
     ok(false, "Promise failed: " + err);
     if (err.stack) {
       dump(err.stack);
@@ -207,10 +218,6 @@ function promiseDone(promise) {
 
 // Mutation list testing
 
-function isSrcChange(change) {
-  return (change.type === "attributes" && change.attributeName === "src");
-}
-
 function assertAndStrip(mutations, message, test) {
   let size = mutations.length;
   mutations = mutations.filter(test);
@@ -245,7 +252,8 @@ function isNewRoot(change) {
 // Make sure an iframe's src attribute changed and then
 // strip that mutation out of the list.
 function assertSrcChange(mutations) {
-  return assertAndStrip(mutations, "Should have had an iframe source change.", isSrcChange);
+  return assertAndStrip(mutations, "Should have had an iframe source change.",
+                        isSrcChange);
 }
 
 // Make sure there's an unload in the mutation list and strip
@@ -285,7 +293,6 @@ function waitForMutation(walker, test, mutations = []) {
   return deferred.promise;
 }
 
-
 var _tests = [];
 function addTest(test) {
   _tests.push(test);
@@ -300,7 +307,7 @@ function runNextTest() {
     SimpleTest.finish();
     return;
   }
-  var fn = _tests.shift();
+  let fn = _tests.shift();
   try {
     fn();
   } catch (ex) {
diff --git a/devtools/server/tests/mochitest/inspector-search-data.html b/devtools/server/tests/mochitest/inspector-search-data.html
index d0d5f9c68b3a..4ca0ba9ac98b 100644
--- a/devtools/server/tests/mochitest/inspector-search-data.html
+++ b/devtools/server/tests/mochitest/inspector-search-data.html
@@ -15,8 +15,10 @@
     }
   </style>
   <script type="text/javascript">
-    window.onload = function() {
-      window.opener.postMessage('ready', '*');
+    "use strict";
+
+    window.onload = function () {
+      window.opener.postMessage("ready", "*");
     };
   </script>
 </head>
@@ -49,4 +51,4 @@
 
   <div class="💩" id="💩" 💩="💩"></div>
 </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/devtools/server/tests/mochitest/inspector-styles-data.html b/devtools/server/tests/mochitest/inspector-styles-data.html
index a2a126f0e199..029050167399 100644
--- a/devtools/server/tests/mochitest/inspector-styles-data.html
+++ b/devtools/server/tests/mochitest/inspector-styles-data.html
@@ -1,8 +1,10 @@
 <html>
 <script>
+  "use strict";
+
   window.onload = () => {
-    window.opener.postMessage('ready', '*')
-  }
+    window.opener.postMessage("ready", "*");
+  };
 </script>
 <style>
   .inheritable-rule {
diff --git a/devtools/server/tests/mochitest/inspector-traversal-data.html b/devtools/server/tests/mochitest/inspector-traversal-data.html
index 840b444a5314..c073897e8aef 100644
--- a/devtools/server/tests/mochitest/inspector-traversal-data.html
+++ b/devtools/server/tests/mochitest/inspector-traversal-data.html
@@ -18,26 +18,27 @@
     }
   </style>
   <script type="text/javascript">
-    window.onload = function() {
+    "use strict";
 
+    window.onload = function () {
       // Set up a basic shadow DOM
-      var host = document.querySelector('#shadow');
+      let host = document.querySelector("#shadow");
       if (host.createShadowRoot) {
-        var root = host.createShadowRoot();
-        root.innerHTML = '<h3>Shadow <em>DOM</em></h3><select multiple></select>';
+        let root = host.createShadowRoot();
+        root.innerHTML = "<h3>Shadow <em>DOM</em></h3><select multiple></select>";
       }
 
       // Put a copy of the body in an iframe to test frame traversal.
-      var body = document.querySelector("body");
-      var data = "data:text/html,<html>" + body.outerHTML + "<html>";
-      var iframe = document.createElement("iframe");
+      let body = document.querySelector("body");
+      let data = "data:text/html,<html>" + body.outerHTML + "<html>";
+      let iframe = document.createElement("iframe");
       iframe.setAttribute("id", "childFrame");
-      iframe.onload = function() {
-        window.opener.postMessage('ready', '*')
+      iframe.onload = function () {
+        window.opener.postMessage("ready", "*");
       };
       iframe.src = data;
       body.appendChild(iframe);
-    }
+    };
   </script>
 </head>
 <body style="background-color:white">
diff --git a/devtools/server/tests/mochitest/inspector_css-properties.html b/devtools/server/tests/mochitest/inspector_css-properties.html
index 2c160c92803f..dcbec597ac86 100644
--- a/devtools/server/tests/mochitest/inspector_css-properties.html
+++ b/devtools/server/tests/mochitest/inspector_css-properties.html
@@ -2,8 +2,10 @@
 <head>
 <body>
   <script type="text/javascript">
-    window.onload = function() {
-      window.opener.postMessage('ready', '*');
+    "use strict";
+
+    window.onload = function () {
+      window.opener.postMessage("ready", "*");
     };
   </script>
 </body>
diff --git a/devtools/server/tests/mochitest/inspector_getImageData.html b/devtools/server/tests/mochitest/inspector_getImageData.html
index eebecea9070f..02d2b4d28f29 100644
--- a/devtools/server/tests/mochitest/inspector_getImageData.html
+++ b/devtools/server/tests/mochitest/inspector_getImageData.html
@@ -7,6 +7,8 @@
   <img class="small" src="small-image.gif">
   <img class="data" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABwAAAAcCAYAAAByDd+UAAAAJklEQVRIie3NMREAAAgAoe9fWls4eAzMVM0xoVAoFAqFQqFQ+C9chp4NHvu+4Q4AAAAASUVORK5CYII=">
   <script>
+    "use strict";
+
     window.onload = () => {
       var canvas = document.querySelector("canvas"), ctx = canvas.getContext("2d");
       canvas.width = 1000;
@@ -14,8 +16,8 @@
       ctx.fillStyle = "red";
       ctx.fillRect(0, 0, 1000, 2000);
 
-      window.opener.postMessage('ready', '*')
-    }
+      window.opener.postMessage("ready", "*");
+    };
   </script>
 </body>
 </html>
diff --git a/devtools/server/tests/mochitest/memory-helpers.js b/devtools/server/tests/mochitest/memory-helpers.js
index aea8c4732400..e100a3b06a88 100644
--- a/devtools/server/tests/mochitest/memory-helpers.js
+++ b/devtools/server/tests/mochitest/memory-helpers.js
@@ -1,14 +1,16 @@
-var Cu = Components.utils;
-var Cc = Components.classes;
-var Ci = Components.interfaces;
+/* exported Task, startServerAndGetSelectedTabMemory, destroyServerAndFinish,
+   waitForTime, waitUntil */
+"use strict";
 
-var { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
+const Cu = Components.utils;
+
+const { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
+const Services = require("Services");
 const { Task } = require("devtools/shared/task");
-var Services = require("Services");
-var { DebuggerClient } = require("devtools/shared/client/main");
-var { DebuggerServer } = require("devtools/server/main");
+const { DebuggerClient } = require("devtools/shared/client/main");
+const { DebuggerServer } = require("devtools/server/main");
 
-var { MemoryFront } = require("devtools/shared/fronts/memory");
+const { MemoryFront } = require("devtools/shared/fronts/memory");
 
 // Always log packets when running tests.
 Services.prefs.setBoolPref("devtools.debugger.log", true);
@@ -19,13 +21,13 @@ SimpleTest.registerCleanupFunction(function () {
 function startServerAndGetSelectedTabMemory() {
   DebuggerServer.init();
   DebuggerServer.addBrowserActors();
-  var client = new DebuggerClient(DebuggerServer.connectPipe());
+  let client = new DebuggerClient(DebuggerServer.connectPipe());
 
   return client.connect()
     .then(() => client.listTabs())
     .then(response => {
-      var form = response.tabs[response.selected];
-      var memory = MemoryFront(client, form, response);
+      let form = response.tabs[response.selected];
+      let memory = MemoryFront(client, form, response);
 
       return { memory, client };
     });
@@ -48,5 +50,6 @@ function waitUntil(predicate) {
   if (predicate()) {
     return Promise.resolve(true);
   }
-  return new Promise(resolve => setTimeout(() => waitUntil(predicate).then(() => resolve(true)), 10));
+  return new Promise(resolve => setTimeout(() => waitUntil(predicate)
+         .then(() => resolve(true)), 10));
 }
diff --git a/devtools/server/tests/mochitest/nonchrome_unsafeDereference.html b/devtools/server/tests/mochitest/nonchrome_unsafeDereference.html
index 6c19d3104184..15e9fd9160bc 100644
--- a/devtools/server/tests/mochitest/nonchrome_unsafeDereference.html
+++ b/devtools/server/tests/mochitest/nonchrome_unsafeDereference.html
@@ -1,8 +1,10 @@
 <!DOCTYPE HTML>
 <html>
 <script>
-var xhr = new XMLHttpRequest;
+"use strict";
+
+var xhr = new XMLHttpRequest();
 xhr.timeout = 1742;
-xhr.expando = 'Expando!';
+xhr.expando = "Expando!";
 </script>
 </html>
diff --git a/devtools/server/tests/mochitest/setup-in-child.js b/devtools/server/tests/mochitest/setup-in-child.js
index a575faa20ac5..b5614ab1e19c 100644
--- a/devtools/server/tests/mochitest/setup-in-child.js
+++ b/devtools/server/tests/mochitest/setup-in-child.js
@@ -1,6 +1,8 @@
+"use strict";
+
 const {Cc, Ci} = require("chrome");
-const cpmm = Cc["@mozilla.org/childprocessmessagemanager;1"].
-  getService(Ci.nsIMessageListenerManager);
+const cpmm = Cc["@mozilla.org/childprocessmessagemanager;1"]
+             .getService(Ci.nsIMessageListenerManager);
 const { DebuggerServer } = require("devtools/server/main");
 
 exports.setupChild = function (a, b, c) {
diff --git a/devtools/server/tests/mochitest/setup-in-parent.js b/devtools/server/tests/mochitest/setup-in-parent.js
index 9845ee647901..65a65897e358 100644
--- a/devtools/server/tests/mochitest/setup-in-parent.js
+++ b/devtools/server/tests/mochitest/setup-in-parent.js
@@ -1,3 +1,5 @@
+"use strict";
+
 var {Ci} = require("chrome");
 var Services = require("Services");
 
diff --git a/devtools/server/tests/mochitest/test_Debugger.Script.prototype.global.html b/devtools/server/tests/mochitest/test_Debugger.Script.prototype.global.html
index 77357e608358..ab20610afb0d 100644
--- a/devtools/server/tests/mochitest/test_Debugger.Script.prototype.global.html
+++ b/devtools/server/tests/mochitest/test_Debugger.Script.prototype.global.html
@@ -14,6 +14,7 @@ Debugger.Script.prototype.global should return innerize globals, not WindowProxi
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 Components.utils.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
@@ -21,27 +22,26 @@ addDebuggerToGlobal(this);
 window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var iframe = document.createElement("iframe");
+  let iframe = document.createElement("iframe");
   iframe.src = "data:text/html,<script>function glorp() { }<\/script>";
   iframe.onload = firstOnLoadHandler;
   document.body.appendChild(iframe);
 
   function firstOnLoadHandler() {
-    var dbg = new Debugger;
-    var iframeDO = dbg.addDebuggee(iframe.contentWindow);
+    let dbg = new Debugger();
+    let iframeDO = dbg.addDebuggee(iframe.contentWindow);
 
     // For sanity: check that the debuggee global is the inner window,
     // and that the outer window gets a distinct D.O.
-    var iframeWindowProxyDO = iframeDO.makeDebuggeeValue(iframe.contentWindow);
+    let iframeWindowProxyDO = iframeDO.makeDebuggeeValue(iframe.contentWindow);
     ok(iframeDO !== iframeWindowProxyDO);
 
     // The real test: Debugger.Script.prototype.global returns inner windows.
-    ok(iframeDO.getOwnPropertyDescriptor('glorp').value.script.global === iframeDO);
+    ok(iframeDO.getOwnPropertyDescriptor("glorp").value.script.global === iframeDO);
 
     SimpleTest.finish();
   }
-}
-
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_Debugger.Source.prototype.element.html b/devtools/server/tests/mochitest/test_Debugger.Source.prototype.element.html
index 3cbc223539d3..b1d223f93eda 100644
--- a/devtools/server/tests/mochitest/test_Debugger.Source.prototype.element.html
+++ b/devtools/server/tests/mochitest/test_Debugger.Source.prototype.element.html
@@ -15,6 +15,7 @@ element to which code is attached (if any), and how.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 Components.utils.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
@@ -22,65 +23,65 @@ addDebuggerToGlobal(this);
 window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var log = '';
-  var doc, dieter, ulrich, isolde, albrecht;
-  var dbg, iframeDO, DOFor;
+  let log = "";
+  let doc, dieter, ulrich, isolde, albrecht;
+  let dbg, iframeDO, DOFor;
 
   // Create an iframe to debug.
   // We can't use a data: URL here, because we want to test script elements
   // that refer to the JavaScript via 'src' attributes, and data: documents
   // can't refer to those. So we use a separate HTML document.
-  var iframe = document.createElement("iframe");
+  let iframe = document.createElement("iframe");
   iframe.src = "Debugger.Source.prototype.element.html";
   iframe.onload = onLoadHandler;
   document.body.appendChild(iframe);
 
   function onLoadHandler() {
-    log += 'l';
+    log += "l";
 
     // Now that the iframe's window has been created, we can add
     // it as a debuggee.
-    dbg = new Debugger;
+    dbg = new Debugger();
     dbg.onDebuggerStatement = franzDebuggerHandler;
     iframeDO = dbg.addDebuggee(iframe.contentWindow);
     DOFor = iframeDO.makeDebuggeeValue.bind(iframeDO);
 
     // Send a click event to heidi.
     doc = iframe.contentWindow.document;
-    doc.getElementById('heidi').dispatchEvent(new Event('click'));
+    doc.getElementById("heidi").dispatchEvent(new Event("click"));
   }
 
   function franzDebuggerHandler(frame) {
-    log += 'f';
+    log += "f";
 
     // The top stack frame should be franz, belonging to the script element.
-    ok(frame.callee.displayName === 'franz', 'top frame is franz');
-    ok(frame.script.source.element === DOFor(doc.getElementById('franz')),
-       'top frame source belongs to element franz');
+    ok(frame.callee.displayName === "franz", "top frame is franz");
+    ok(frame.script.source.element === DOFor(doc.getElementById("franz")),
+       "top frame source belongs to element franz");
     ok(frame.script.source.elementAttributeName === undefined,
        "top frame source doesn't belong to an attribute");
 
     // The second stack frame should belong to heinrich.
-    ok(frame.older.script.source.element === DOFor(doc.getElementById('heinrich')),
+    ok(frame.older.script.source.element === DOFor(doc.getElementById("heinrich")),
        "second frame source belongs to element heinrich");
     ok(frame.older.script.source.elementAttributeName === undefined,
        "second frame source doesn't belong to an attribute");
 
     // The next stack frame should belong to heidi's onclick handler.
-    ok(frame.older.older.script.source.element === DOFor(doc.getElementById('heidi')),
-       'third frame source belongs to element heidi');
-    ok(frame.older.older.script.source.elementAttributeName === 'onclick',
+    ok(frame.older.older.script.source.element === DOFor(doc.getElementById("heidi")),
+       "third frame source belongs to element heidi");
+    ok(frame.older.older.script.source.elementAttributeName === "onclick",
        "third frame source belongs to 'onclick' attribute");
 
     // Try a dynamically inserted inline script element.
-    ulrich = doc.createElement('script');
-    ulrich.text = 'debugger;'
+    ulrich = doc.createElement("script");
+    ulrich.text = "debugger;";
     dbg.onDebuggerStatement = ulrichDebuggerHandler;
     doc.body.appendChild(ulrich);
   }
 
   function ulrichDebuggerHandler(frame) {
-    log += 'u';
+    log += "u";
 
     // The top frame should be ulrich's text.
     ok(frame.script.source.element === DOFor(ulrich),
@@ -89,23 +90,23 @@ window.onload = function () {
        "top frame is not on an attribute of ulrich");
 
     // Try a dynamically inserted out-of-line script element.
-    isolde = doc.createElement('script');
-    isolde.setAttribute('src', 'Debugger.Source.prototype.element-2.js');
-    isolde.setAttribute('id', 'idolde, my dear');
+    isolde = doc.createElement("script");
+    isolde.setAttribute("src", "Debugger.Source.prototype.element-2.js");
+    isolde.setAttribute("id", "idolde, my dear");
     dbg.onDebuggerStatement = isoldeDebuggerHandler;
     doc.body.appendChild(isolde);
   }
 
   function isoldeDebuggerHandler(frame) {
-    log += 'i';
+    log += "i";
 
     // The top frame should belong to isolde.
     ok(frame.script.source.element === DOFor(isolde),
        "top frame belongs to isolde");
     info("frame.script.source.element is: " + uneval(frame.script.source.element));
-    if (typeof frame.script.source.element.unsafeDereference() == 'object') {
-       info("   toString: " + frame.script.source.element.unsafeDereference());
-       info("   id: " + frame.script.source.element.unsafeDereference().id);
+    if (typeof frame.script.source.element.unsafeDereference() == "object") {
+      info("   toString: " + frame.script.source.element.unsafeDereference());
+      info("   id: " + frame.script.source.element.unsafeDereference().id);
     }
 
     ok(frame.script.source.elementAttributeName === undefined,
@@ -114,20 +115,20 @@ window.onload = function () {
          uneval(frame.script.source.elementAttributeName));
 
     // Try a dynamically created div element with a handler.
-    dieter = doc.createElement('div');
-    dieter.setAttribute('id', 'dieter');
-    dieter.setAttribute('ondrag', 'debugger;');
+    dieter = doc.createElement("div");
+    dieter.setAttribute("id", "dieter");
+    dieter.setAttribute("ondrag", "debugger;");
     dbg.onDebuggerStatement = dieterDebuggerHandler;
-    dieter.dispatchEvent(new Event('drag'));
- }
+    dieter.dispatchEvent(new Event("drag"));
+  }
 
- function dieterDebuggerHandler(frame) {
-    log += 'd';
+  function dieterDebuggerHandler(frame) {
+    log += "d";
 
     // The top frame should belong to dieter's ondrag handler.
     ok(frame.script.source.element === DOFor(dieter),
        "second event's handler belongs to dieter");
-    ok(frame.script.source.elementAttributeName === 'ondrag',
+    ok(frame.script.source.elementAttributeName === "ondrag",
        "second event's handler is on dieter's 'ondrag' element");
 
     // Try sending an 'onresize' event to the window.
@@ -139,43 +140,42 @@ window.onload = function () {
     // won't affect propagation. Then, the content event only runs its
     // 'debugger' statement when the event is cancelable. It's a kludge.
     dbg.onDebuggerStatement = resizeDebuggerHandler;
-    iframe.contentWindow.dispatchEvent(new Event('resize', { cancelable: true }));
+    iframe.contentWindow.dispatchEvent(new Event("resize", { cancelable: true }));
   }
 
   function resizeDebuggerHandler(frame) {
-    log += 'e';
+    log += "e";
 
     // The top frame should belong to the body's 'onresize' handler, even
     // though we sent the message to the window and it was handled.
     ok(frame.script.source.element === DOFor(doc.body),
        "onresize event handler belongs to body element");
-    ok(frame.script.source.elementAttributeName === 'onresize',
+    ok(frame.script.source.elementAttributeName === "onresize",
        "onresize event handler is on body element's 'onresize' attribute");
 
     // In SVG, the event and the attribute that holds that event's handler
     // have different names. Debugger.Source.prototype.elementAttributeName
     // should report (as one might infer) the attribute name, not the event
     // name.
-    albrecht = doc.createElementNS('http://www.w3.org/2000/svg', 'svg');
-    albrecht.setAttribute('onload', 'debugger;');
+    albrecht = doc.createElementNS("http://www.w3.org/2000/svg", "svg");
+    albrecht.setAttribute("onload", "debugger;");
     dbg.onDebuggerStatement = SVGLoadHandler;
     albrecht.dispatchEvent(new Event("SVGLoad"));
   }
 
   function SVGLoadHandler(frame) {
-    log += 's';
+    log += "s";
 
     // The top frame's source should be on albrecht's 'onload' attribute.
     ok(frame.script.source.element === DOFor(albrecht),
        "SVGLoad event handler belongs to albrecht");
-    ok(frame.script.source.elementAttributeName === 'onload',
+    ok(frame.script.source.elementAttributeName === "onload",
        "SVGLoad event handler is on albrecht's 'onload' attribute");
 
-    ok(log === 'lfuides', "all tests actually ran");
+    ok(log === "lfuides", "all tests actually ran");
     SimpleTest.finish();
   }
-}
-
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionScript.html b/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionScript.html
index cbc2ae6155d3..ed186475f5af 100644
--- a/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionScript.html
+++ b/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionScript.html
@@ -15,6 +15,7 @@ behave when 'eval' is called with no scripted frames active at all.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 Components.utils.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
@@ -22,10 +23,10 @@ addDebuggerToGlobal(this);
 window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var dbg, iframeDO, doc, script2DO;
+  let dbg, iframeDO, doc, script2DO;
 
   // Create an iframe to debug.
-  var iframe = document.createElement("iframe");
+  let iframe = document.createElement("iframe");
   iframe.src = "data:text/html,<div>Hi!</div>";
   iframe.onload = onLoadHandler;
   document.body.appendChild(iframe);
@@ -33,11 +34,11 @@ window.onload = function () {
   function onLoadHandler() {
     // Now that the iframe's window has been created, we can add
     // it as a debuggee.
-    dbg = new Debugger;
+    dbg = new Debugger();
     iframeDO = dbg.addDebuggee(iframe.contentWindow);
 
     doc = iframe.contentWindow.document;
-    var script = doc.createElement('script');
+    let script = doc.createElement("script");
     script.text = "setTimeout(eval.bind(null, 'debugger;'), 0);";
     dbg.onDebuggerStatement = timerHandler;
     doc.body.appendChild(script);
@@ -46,7 +47,7 @@ window.onload = function () {
   function timerHandler(frame) {
     // The top stack frame's source should have an undefined
     // introduction script and introduction offset.
-    var source = frame.script.source;
+    let source = frame.script.source;
     ok(source.introductionScript === undefined,
        "setTimeout eval introductionScript is undefined");
     ok(source.introductionOffset === undefined,
@@ -55,7 +56,7 @@ window.onload = function () {
     // Check that the above isn't just some quirk of iframes, or the
     // browser milieu destroying information: an eval script should indeed
     // have proper introduction information.
-    var script2 = doc.createElement('script');
+    let script2 = doc.createElement("script");
     script2.text = "eval('debugger;');";
     script2DO = iframeDO.makeDebuggeeValue(script2);
     dbg.onDebuggerStatement = evalHandler;
@@ -65,10 +66,10 @@ window.onload = function () {
   function evalHandler(frame) {
     // The top stack frame's source should be introduced by the script that
     // called eval.
-    var source = frame.script.source;
-    var frame2 = frame.older;
+    let source = frame.script.source;
+    let frame2 = frame.older;
 
-    ok(source.introductionType === 'eval',
+    ok(source.introductionType === "eval",
        "top frame's source was introduced by 'eval'");
     ok(source.introductionScript === frame2.script,
        "eval frame's introduction script is the older frame's script");
@@ -81,7 +82,7 @@ window.onload = function () {
     // information. (In the future, we certainly could point at the call
     // that inserted the script element into the document; if that happens,
     // we can update this test.)
-    ok(frame2.script.source.introductionType === 'scriptElement',
+    ok(frame2.script.source.introductionType === "scriptElement",
        "older frame has no introduction type");
     ok(frame2.script.source.introductionScript === undefined,
        "older frame has no introduction script");
@@ -90,7 +91,7 @@ window.onload = function () {
 
     SimpleTest.finish();
   }
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionType.html b/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionType.html
index 6f5be33f51bd..98c71e594abe 100644
--- a/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionType.html
+++ b/devtools/server/tests/mochitest/test_Debugger.Source.prototype.introductionType.html
@@ -16,13 +16,14 @@ JavaScrip appearing in an inline event handler attribute.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 Components.utils.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
 
-var dbg;
-var iframeDO, doc;
-var Tootles, TootlesDO;
+let dbg;
+let iframeDO, doc;
+let Tootles, TootlesDO;
 
 window.onload = function () {
   SimpleTest.waitForExplicitFinish();
@@ -31,7 +32,7 @@ window.onload = function () {
 
 addTest(function setup() {
   // Create an iframe to debug.
-  var iframe = document.createElement("iframe");
+  let iframe = document.createElement("iframe");
   iframe.src = "data:text/html," +
                "<div id='Tootles' onclick='debugger;'>I'm a DIV!</div>" +
                "<script id='Auddie'>function auddie() { debugger; }<\/script>";
@@ -41,88 +42,84 @@ addTest(function setup() {
   function onLoadHandler() {
     // Now that the iframe's window has been created, we can add
     // it as a debuggee.
-    dbg = new Debugger;
+    dbg = new Debugger();
     iframeDO = dbg.addDebuggee(iframe.contentWindow);
     doc = iframe.contentWindow.document;
-    Tootles = doc.getElementById('Tootles');
+    Tootles = doc.getElementById("Tootles");
     TootlesDO = iframeDO.makeDebuggeeValue(Tootles);
 
     runNextTest();
   }
 });
 
-
 // Check the introduction type of in-markup event handler code.
 // Send a click event to Tootles, whose handler has a 'debugger' statement,
 // and check that script's introduction type.
 addTest(function ClickOnTootles() {
   dbg.onDebuggerStatement = TootlesClickDebugger;
-  Tootles.dispatchEvent(new Event('click'));
+  Tootles.dispatchEvent(new Event("click"));
 
   function TootlesClickDebugger(frame) {
     // some sanity checks
     ok(frame.script.source.element === TootlesDO,
        "top frame source belongs to element 'Tootles'");
-    is(frame.script.source.elementAttributeName, 'onclick',
+    is(frame.script.source.elementAttributeName, "onclick",
        "top frame source belongs to 'onclick' attribute");
 
     // And, the actual point of this test:
-    is(frame.script.source.introductionType, 'eventHandler',
+    is(frame.script.source.introductionType, "eventHandler",
        "top frame source's introductionType is 'eventHandler'");
 
     runNextTest();
   }
 });
 
-
 // Check the introduction type of dynamically added event handler code.
 // Add a drag event handler to Tootles as a string, and then send
 // Tootles a drag event.
 addTest(function DragTootles() {
   dbg.onDebuggerStatement = TootlesDragDebugger;
-  Tootles.setAttribute('ondrag', 'debugger;');
-  Tootles.dispatchEvent(new Event('drag'));
+  Tootles.setAttribute("ondrag", "debugger;");
+  Tootles.dispatchEvent(new Event("drag"));
 
   function TootlesDragDebugger(frame) {
     // sanity checks
     ok(frame.script.source.element === TootlesDO,
        "top frame source belongs to element 'Tootles'");
-    is(frame.script.source.elementAttributeName, 'ondrag',
+    is(frame.script.source.elementAttributeName, "ondrag",
        "top frame source belongs to 'ondrag' attribute");
 
     // And, the actual point of this test:
-    is(frame.script.source.introductionType, 'eventHandler',
+    is(frame.script.source.introductionType, "eventHandler",
        "top frame source's introductionType is 'eventHandler'");
 
     runNextTest();
   }
 });
 
-
 // Check the introduction type of an in-markup script element.
 addTest(function checkAuddie() {
-  var fnDO = iframeDO.getOwnPropertyDescriptor('auddie').value;
-  var AuddieDO = iframeDO.makeDebuggeeValue(doc.getElementById('Auddie'));
+  let fnDO = iframeDO.getOwnPropertyDescriptor("auddie").value;
+  let AuddieDO = iframeDO.makeDebuggeeValue(doc.getElementById("Auddie"));
 
-  is(fnDO.class, 'Function',
+  is(fnDO.class, "Function",
      "Script element 'Auddie' defined function 'auddie'.");
   ok(fnDO.script.source.element === AuddieDO,
      "Function auddie's script belongs to script element 'Auddie'");
   is(fnDO.script.source.elementAttributeName, undefined,
      "Function auddie's script doesn't belong to any attribute of 'Auddie'");
-  is(fnDO.script.source.introductionType, 'scriptElement',
+  is(fnDO.script.source.introductionType, "scriptElement",
      "Function auddie's script's source was introduced by a script element");
 
   runNextTest();
 });
 
-
 // Check the introduction type of a dynamically inserted script element.
 addTest(function InsertRover() {
   dbg.onDebuggerStatement = RoverDebugger;
-  var rover = doc.createElement('script');
-  var roverDO = iframeDO.makeDebuggeeValue(rover);
-  rover.text = 'debugger;';
+  let rover = doc.createElement("script");
+  let roverDO = iframeDO.makeDebuggeeValue(rover);
+  rover.text = "debugger;";
   doc.body.appendChild(rover);
 
   function RoverDebugger(frame) {
@@ -133,17 +130,16 @@ addTest(function InsertRover() {
        "Rover script doesn't belong to an attribute of Rover");
 
     // Check the introduction type.
-    ok(frame.script.source.introductionType === 'scriptElement',
+    ok(frame.script.source.introductionType === "scriptElement",
        "Rover script's introduction type is 'scriptElement'");
 
     runNextTest();
   }
 });
 
-
 // Create a XUL document with a script element, and check its introduction type.
 addTest(function XULDocumentScript() {
-  var xulFrame = document.createElement('iframe');
+  let xulFrame = document.createElement("iframe");
   xulFrame.src = "data:application/vnd.mozilla.xul+xml;charset=utf-8," +
                  "<?xml version=\"1.0\"?>" +
                  "<window xmlns='http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul'>" +
@@ -155,12 +151,10 @@ addTest(function XULDocumentScript() {
 
   function xulLoaded() {
     info("Loaded XUL document");
-    var xulFrameDO = dbg.addDebuggee(xulFrame.contentWindow);
-    var xulDoc = xulFrame.contentWindow.document;
-    var xulieDO = xulFrameDO.makeDebuggeeValue(xulDoc.getElementById('xulie'));
-    var xulFnDO = xulFrameDO.getOwnPropertyDescriptor('xulScriptFunc').value;
-    is(typeof xulFnDO, 'object', "XUL script element defined 'xulScriptFunc'");
-    is(xulFnDO.class, 'Function',
+    let xulFrameDO = dbg.addDebuggee(xulFrame.contentWindow);
+    let xulFnDO = xulFrameDO.getOwnPropertyDescriptor("xulScriptFunc").value;
+    is(typeof xulFnDO, "object", "XUL script element defined 'xulScriptFunc'");
+    is(xulFnDO.class, "Function",
        "XUL global 'xulScriptFunc' is indeed a function");
 
     // A XUL document's script elements' code gets shared amongst all
@@ -169,12 +163,11 @@ addTest(function XULDocumentScript() {
     is(xulFnDO.script.source.element, undefined,
        "XUL script code should not be attributed to any individual element");
 
-    is(xulFnDO.script.source.introductionType, 'scriptElement',
+    is(xulFnDO.script.source.introductionType, "scriptElement",
        "xulScriptFunc's introduction type is 'scriptElement'");
     runNextTest();
   }
 });
-
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_animation_actor-lifetime.html b/devtools/server/tests/mochitest/test_animation_actor-lifetime.html
index 158fd42479ef..859d8669469d 100644
--- a/devtools/server/tests/mochitest/test_animation_actor-lifetime.html
+++ b/devtools/server/tests/mochitest/test_animation_actor-lifetime.html
@@ -11,67 +11,65 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1247243
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-window.onload = function() {
-  const Ci = Components.interfaces;
+"use strict";
+
+window.onload = function () {
   const {AnimationsFront} = require("devtools/shared/fronts/animation");
   const {InspectorFront} = require("devtools/shared/fronts/inspector");
 
   SimpleTest.waitForExplicitFinish();
 
   let gWalker = null;
-  let gClient = null;
   let animationsFront = null;
 
   addTest(function setup() {
-    info ("Setting up inspector and animation actors.");
+    info("Setting up inspector and animation actors.");
 
     let url = document.getElementById("animationContent").href;
-    attachURL(url, function(err, client, tab, doc) {
+    attachURL(url, function (err, client, tab, doc) {
       let inspector = InspectorFront(client, tab);
 
       animationsFront = new AnimationsFront(client, tab);
 
       promiseDone(inspector.getWalker().then(walker => {
         ok(walker, "getWalker() should return an actor.");
-        gClient = client;
         gWalker = walker;
       }).then(runNextTest));
-
     });
   });
 
   addAsyncTest(function* testActorLifetime() {
-
-    info ("Testing animated node actor");
+    info("Testing animated node actor");
     let animatedNodeActor = yield gWalker.querySelector(gWalker.rootNode,
       ".animated");
     yield animationsFront.getAnimationPlayersForNode(animatedNodeActor);
 
-    let animationsActor = DebuggerServer._searchAllConnectionsForActor(animationsFront.actorID);
+    let animationsActor = DebuggerServer
+                          ._searchAllConnectionsForActor(animationsFront.actorID);
 
     is(animationsActor.actors.length, 1,
       "AnimationActor have 1 AnimationPlayerActors");
 
-    info ("Testing AnimationPlayerActors release");
+    info("Testing AnimationPlayerActors release");
     let stillNodeActor = yield gWalker.querySelector(gWalker.rootNode,
       ".still");
     yield animationsFront.getAnimationPlayersForNode(stillNodeActor);
     is(animationsActor.actors.length, 0,
       "AnimationActor does not have any AnimationPlayerActors anymore");
 
-    info ("Testing multi animated node actor");
+    info("Testing multi animated node actor");
     let multiNodeActor = yield gWalker.querySelector(gWalker.rootNode,
       ".multi");
     yield animationsFront.getAnimationPlayersForNode(multiNodeActor);
     is(animationsActor.actors.length, 2,
       "AnimationActor has now 2 AnimationPlayerActors");
 
-    info ("Testing single animated node actor");
+    info("Testing single animated node actor");
     yield animationsFront.getAnimationPlayersForNode(animatedNodeActor);
     is(animationsActor.actors.length, 1,
       "AnimationActor has only one AnimationPlayerActors");
 
-    info ("Testing AnimationPlayerActors release again");
+    info("Testing AnimationPlayerActors release again");
     yield animationsFront.getAnimationPlayersForNode(stillNodeActor);
     is(animationsActor.actors.length, 0,
       "AnimationActor does not have any AnimationPlayerActors anymore");
@@ -79,7 +77,6 @@ window.onload = function() {
     runNextTest();
   });
 
-
   runNextTest();
 };
   </script>
diff --git a/devtools/server/tests/mochitest/test_connectToChild.html b/devtools/server/tests/mochitest/test_connectToChild.html
index f9fca4dfb039..fab3a26f59bd 100644
--- a/devtools/server/tests/mochitest/test_connectToChild.html
+++ b/devtools/server/tests/mochitest/test_connectToChild.html
@@ -1,4 +1,4 @@
-<SDOCTYPv HTM.>
+<!DOCTYPE HTML>
 <html>
 <!--
 Bug 966991 - Test DebuggerServer.connectToChild
@@ -12,16 +12,16 @@ Bug 966991 - Test DebuggerServer.connectToChild
 <body>
 <pre id="test">
 <script type="application/javascript">
+"use strict";
 
 let Cu = Components.utils;
-let Cc = Components.classes;
 let Ci = Components.interfaces;
 
 let { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
 let { DebuggerClient } = require("devtools/shared/client/main");
 let { DebuggerServer } = require("devtools/server/main");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   SpecialPowers.pushPrefEnv({
@@ -31,7 +31,7 @@ window.onload = function() {
       ["dom.mozBrowserFramesEnabled", true]
     ]
   }, runTests);
-}
+};
 
 function runTests() {
   // Create a minimal iframe with a message manager
@@ -44,14 +44,18 @@ function runTests() {
   // Register a test actor in the child process so that we can know if and when
   // this fake actor is destroyed.
   mm.loadFrameScript("data:text/javascript,new " + function FrameScriptScope() {
+    /* eslint-disable no-shadow */
     const { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
     const { DebuggerServer } = require("devtools/server/main");
+    /* eslint-enable no-shadow */
 
     if (!DebuggerServer.initialized) {
       DebuggerServer.init();
     }
 
-    function TestActor() {dump("instanciate test actor\n");}
+    function TestActor() {
+      dump("instanciate test actor\n");
+    }
     TestActor.prototype = {
       actorPrefix: "test",
 
@@ -59,7 +63,7 @@ function runTests() {
         sendAsyncMessage("test-actor-destroyed", null);
       },
       hello: function () {
-        return {msg:"world"};
+        return {msg: "world"};
       }
     };
     TestActor.prototype.requestTypes = {
@@ -90,7 +94,6 @@ function runTests() {
         to: actor.testActor,
         type: "hello",
       }, function (response) {
-
         // Then close the client. That should end up cleaning our test actor
         client.close();
 
@@ -113,7 +116,8 @@ function runTests() {
     let client = new DebuggerClient(transport);
     DebuggerServer.connectToChild(conn, iframe).then(actor => {
       ok(actor.testActor, "Got a test actor for the second connection");
-      isnot(actor.testActor, firstActor, "We get different actor instances between two connections");
+      isnot(actor.testActor, firstActor,
+            "We get different actor instances between two connections");
 
       client.close(cleanup);
     });
@@ -122,12 +126,11 @@ function runTests() {
   function cleanup() {
     DebuggerServer.destroy();
     iframe.remove();
-    SimpleTest.finish()
+    SimpleTest.finish();
   }
 
   firstClient();
 }
-
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_connection-manager.html b/devtools/server/tests/mochitest/test_connection-manager.html
index bc802f933133..10ab82f53179 100644
--- a/devtools/server/tests/mochitest/test_connection-manager.html
+++ b/devtools/server/tests/mochitest/test_connection-manager.html
@@ -12,70 +12,89 @@ Bug 898485 - [app manager] Implement an abstract connection manager
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var Cu = Components.utils;
+  const Cu = Components.utils;
 
-  var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-  var {DebuggerServer} = require("devtools/server/main");
-  var Services = require("Services");
+  const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
+  const {DebuggerServer} = require("devtools/server/main");
+  const Services = require("Services");
 
   if (!DebuggerServer.initialized) {
     DebuggerServer.init();
     DebuggerServer.addBrowserActors();
   }
 
-  var {ConnectionManager, Connection} = require("devtools/shared/client/connection-manager");
+  const {
+    ConnectionManager,
+    Connection
+  } = require("devtools/shared/client/connection-manager");
 
-  var orgCount = ConnectionManager.connections.length;
+  let orgCount = ConnectionManager.connections.length;
 
   ConnectionManager.once("new", (event, c) => {
-    is(ConnectionManager.connections[orgCount], c, "new event fired, with correct connection");
+    is(ConnectionManager.connections[orgCount], c,
+       "new event fired, with correct connection");
   });
 
-  var c1 = ConnectionManager.createConnection();
-  var c2 = ConnectionManager.createConnection();
+  let c1 = ConnectionManager.createConnection();
+  let c2 = ConnectionManager.createConnection();
 
   is(ConnectionManager.connections[orgCount], c1, "Connection 1 registered");
   is(ConnectionManager.connections[orgCount + 1], c2, "Connection 2 registered");
 
-  c1.once(Connection.Events.DESTROYED, function() {
+  c1.once(Connection.Events.DESTROYED, function () {
     is(ConnectionManager.connections.length, orgCount + 1, "Connection 1 destroyed");
 
-    var c = c2;
+    let c = c2;
 
-    var eventsRef = "connecting connected disconnecting disconnected host-changed disconnected timeout destroyed";
-    var events = [];
+    let eventsRef = "connecting connected disconnecting disconnected host-changed"
+                    + " disconnected timeout destroyed";
+    let events = [];
 
-    var s = Connection.Status;
+    let s = Connection.Status;
 
     is(c.status, s.DISCONNECTED, "disconnected");
 
-    c.once(Connection.Events.CONNECTING, function(e) { events.push(e); is(c.status, s.CONNECTING, "connecting"); });
-    c.once(Connection.Events.CONNECTED, function(e) { events.push(e); is(c.status, s.CONNECTED, "connected"); c.disconnect()});
-    c.once(Connection.Events.DISCONNECTING, function(e) { events.push(e); is(c.status, s.DISCONNECTING, "disconnecting"); });
-    c.once(Connection.Events.DISCONNECTED, function(e) { events.push(e); is(c.status, s.DISCONNECTED, "disconnected"); testError()});
-    c.once(Connection.Events.DESTROYED, function(e) { events.push(e); is(c.status, s.DESTROYED, "destroyed"); finish()});
+    c.once(Connection.Events.CONNECTING, function (e) {
+      events.push(e);
+      is(c.status, s.CONNECTING, "connecting");
+    });
+
+    c.once(Connection.Events.CONNECTED, function (e) {
+      events.push(e);
+      is(c.status, s.CONNECTED, "connected");
+      c.disconnect();
+    });
+
+    c.once(Connection.Events.DISCONNECTING, function (e) {
+      events.push(e);
+      is(c.status, s.DISCONNECTING, "disconnecting");
+    });
+
+    c.once(Connection.Events.DISCONNECTED, function (e) {
+      events.push(e);
+      is(c.status, s.DISCONNECTED, "disconnected");
+      testError();
+    });
+
+    c.once(Connection.Events.DESTROYED, function (e) {
+      events.push(e);
+      is(c.status, s.DESTROYED, "destroyed");
+      finish();
+    });
 
     c.connect();
 
-    function testStore() {
-      c.store.on("set", function(e,path) {
-        if (path.join(".") == "device.width") {
-          is(c.store.object.device.width, window.screen.width, "Store is fed with valid data");
-          c.disconnect();
-        }
-      });
-    }
-
     function testError() {
-      c.once(Connection.Events.DISCONNECTED, function(e) {
+      c.once(Connection.Events.DISCONNECTED, function (e) {
         events.push(e);
         testKeepConnecting();
       });
-      c.once(Connection.Events.HOST_CHANGED, function(e) {
+      c.once(Connection.Events.HOST_CHANGED, function (e) {
         events.push(e);
         c.connect();
       });
@@ -86,16 +105,17 @@ window.onload = function() {
     function testKeepConnecting() {
       // ensure that keepConnecting keep trying connecting
       // until the connection attempts timeout
-      var originalTimeout = Services.prefs.getIntPref("devtools.debugger.remote-timeout");
+      let prefRemoteTimeout = "devtools.debugger.remote-timeout";
+      let originalTimeout = Services.prefs.getIntPref(prefRemoteTimeout);
       Services.prefs.setIntPref("devtools.debugger.remote-timeout", 1000);
       c.once("timeout", function (e) {
         events.push(e);
-        Services.prefs.setIntPref("devtools.debugger.remote-timeout", originalTimeout);
+        Services.prefs.setIntPref(prefRemoteTimeout, originalTimeout);
         ConnectionManager.destroyConnection(c);
       });
       c.keepConnecting = true;
-      var port = ConnectionManager.getFreeTCPPort();
-      ok(parseInt(port), "Free TCP port looks like a port number");
+      let port = ConnectionManager.getFreeTCPPort();
+      ok(parseInt(port, 10), "Free TCP port looks like a port number");
       c.port = port;
       c.host = "locahost";
       c.connect();
@@ -106,13 +126,10 @@ window.onload = function() {
       DebuggerServer.destroy();
       SimpleTest.finish();
     }
-
   });
 
   ConnectionManager.destroyConnection(c1);
-
-
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_css-logic-media-queries.html b/devtools/server/tests/mochitest/test_css-logic-media-queries.html
index 089ee97c7e8e..5daba9dc7b1f 100644
--- a/devtools/server/tests/mochitest/test_css-logic-media-queries.html
+++ b/devtools/server/tests/mochitest/test_css-logic-media-queries.html
@@ -25,14 +25,15 @@ Test that css-logic handles media-queries correctly
 <body>
   <div></div>
   <script type="application/javascript">
+  "use strict";
 
-  window.onload = function() {
-    var { classes: Cc, utils: Cu, interfaces: Ci } = Components;
+  window.onload = function () {
+    const { classes: Cc, utils: Cu, interfaces: Ci } = Components;
     const DOMUtils = Cc["@mozilla.org/inspector/dom-utils;1"]
       .getService(Ci.inIDOMUtils);
 
-    var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-    var Services = require("Services");
+    const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
+    const Services = require("Services");
     const {CssLogic} = require("devtools/server/css-logic");
 
     SimpleTest.waitForExplicitFinish();
@@ -55,8 +56,7 @@ Test that css-logic handles media-queries correctly
       "rule.source gives correct output for rule 2");
 
     SimpleTest.finish();
-  }
-
+  };
   </script>
 </body>
 </html>
diff --git a/devtools/server/tests/mochitest/test_css-logic-specificity.html b/devtools/server/tests/mochitest/test_css-logic-specificity.html
index 8df0a8fdabc0..430e565aeb98 100644
--- a/devtools/server/tests/mochitest/test_css-logic-specificity.html
+++ b/devtools/server/tests/mochitest/test_css-logic-specificity.html
@@ -10,9 +10,10 @@ Test that css-logic calculates CSS specificity properly
 </head>
 <body style="background:blue;">
   <script type="application/javascript">
+  "use strict";
 
-  window.onload = function() {
-    var {utils: Cu, classes: Cc, interfaces: Ci} = Components;
+  window.onload = function () {
+    const {utils: Cu, classes: Cc, interfaces: Ci} = Components;
 
     const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
     const {CssLogic, CssSelector} = require("devtools/server/css-logic");
@@ -58,7 +59,7 @@ Test that css-logic calculates CSS specificity properly
     let cssRule = cssSheet.domSheet.cssRules[0];
     let selectors = CssLogic.getSelectors(cssRule);
 
-    info("Iterating over the test selectors")
+    info("Iterating over the test selectors");
     for (let i = 0; i < selectors.length; i++) {
       let selectorText = selectors[i];
       info("Testing selector " + selectorText);
@@ -66,7 +67,7 @@ Test that css-logic calculates CSS specificity properly
       let selector = new CssSelector(cssRule, selectorText, i);
       let expected = getExpectedSpecificity(selectorText);
       let specificity = DOMUtils.getSpecificity(selector.cssRule,
-                                                selector.selectorIndex)
+                                                selector.selectorIndex);
       is(specificity, expected,
         'Selector "' + selectorText + '" has a specificity of ' + expected);
     }
@@ -77,8 +78,7 @@ Test that css-logic calculates CSS specificity properly
        "Element styles have specificity of 0x01000000 (16777216).");
 
     SimpleTest.finish();
-  }
-
+  };
   </script>
 </body>
 </html>
diff --git a/devtools/server/tests/mochitest/test_css-logic.html b/devtools/server/tests/mochitest/test_css-logic.html
index 873ec736eae3..a0c00b5eb947 100644
--- a/devtools/server/tests/mochitest/test_css-logic.html
+++ b/devtools/server/tests/mochitest/test_css-logic.html
@@ -11,49 +11,51 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
+"use strict";
+
 const {CssLogic} = require("devtools/server/css-logic");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
 addTest(function getComputedStyle() {
   let node = document.querySelector("#computed-style");
-  is (CssLogic.getComputedStyle(node).getPropertyValue("width"),
+  is(CssLogic.getComputedStyle(node).getPropertyValue("width"),
       "50px", "Computed style on a normal node works (width)");
-  is (CssLogic.getComputedStyle(node).getPropertyValue("height"),
+  is(CssLogic.getComputedStyle(node).getPropertyValue("height"),
       "10px", "Computed style on a normal node works (height)");
 
   let firstChild = new _documentWalker(node, window).firstChild();
-  is (CssLogic.getComputedStyle(firstChild).getPropertyValue("content"),
-      "\"before\"", "Computed style on a ::before node works (content)");
+  is(CssLogic.getComputedStyle(firstChild).getPropertyValue("content"),
+     "\"before\"", "Computed style on a ::before node works (content)");
   let lastChild = new _documentWalker(node, window).lastChild();
-  is (CssLogic.getComputedStyle(lastChild).getPropertyValue("content"),
-      "\"after\"", "Computed style on a ::after node works (content)");
+  is(CssLogic.getComputedStyle(lastChild).getPropertyValue("content"),
+     "\"after\"", "Computed style on a ::after node works (content)");
 
   runNextTest();
 });
 
 addTest(function getBindingElementAndPseudo() {
   let node = document.querySelector("#computed-style");
-  var {bindingElement, pseudo} = CssLogic.getBindingElementAndPseudo(node);
+  let {bindingElement, pseudo} = CssLogic.getBindingElementAndPseudo(node);
 
-  is (bindingElement, node,
-      "Binding element is the node itself for a normal node");
-  ok (!pseudo, "Pseudo is null for a normal node");
+  is(bindingElement, node,
+     "Binding element is the node itself for a normal node");
+  ok(!pseudo, "Pseudo is null for a normal node");
 
   let firstChild = new _documentWalker(node, window).firstChild();
-  var {bindingElement, pseudo} = CssLogic.getBindingElementAndPseudo(firstChild);
-  is (bindingElement, node,
-      "Binding element is the parent for a pseudo node");
-  is (pseudo, ":before", "Pseudo is correct for a ::before node");
+  ({ bindingElement, pseudo } = CssLogic.getBindingElementAndPseudo(firstChild));
+  is(bindingElement, node,
+     "Binding element is the parent for a pseudo node");
+  is(pseudo, ":before", "Pseudo is correct for a ::before node");
 
   let lastChild = new _documentWalker(node, window).lastChild();
-  var {bindingElement, pseudo} = CssLogic.getBindingElementAndPseudo(lastChild);
-  is (bindingElement, node,
-      "Binding element is the parent for a pseudo node");
-  is (pseudo, ":after", "Pseudo is correct for a ::after node");
+  ({ bindingElement, pseudo } = CssLogic.getBindingElementAndPseudo(lastChild));
+  is(bindingElement, node,
+     "Binding element is the parent for a pseudo node");
+  is(pseudo, ":after", "Pseudo is correct for a ::after node");
 
   runNextTest();
 });
diff --git a/devtools/server/tests/mochitest/test_css-properties.html b/devtools/server/tests/mochitest/test_css-properties.html
index f0a44f287779..b3ce226e4d78 100644
--- a/devtools/server/tests/mochitest/test_css-properties.html
+++ b/devtools/server/tests/mochitest/test_css-properties.html
@@ -10,19 +10,21 @@ Bug 1265798 - Replace inIDOMUtils.cssPropertyIsShorthand
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   const { initCssProperties, getCssProperties } =
     require("devtools/shared/fronts/css-properties");
 
-  function promiseAttachUrl (url) {
+  function promiseAttachUrl(url) {
     return new Promise((resolve, reject) => {
-      attachURL(url, function(err, client, tab, doc) {
+      attachURL(url, function (err, client, tab, doc) {
         if (err) {
           return reject(err);
         }
-        resolve({client, tab, doc});
+        return resolve({client, tab, doc});
       });
-    })
+    });
   }
 
   function toSortedString(array) {
@@ -63,7 +65,7 @@ window.onload = function() {
     is(cssProperties, cssPropertiesA,
        "Multiple calls with the same toolbox returns the same object.");
     isnot(cssProperties, cssPropertiesB,
-       "Multiple calls with the different toolboxes return different "+
+       "Multiple calls with the different toolboxes return different " +
        " objects.");
 
     ok(cssProperties.isKnown("border"),
@@ -81,13 +83,13 @@ window.onload = function() {
     ok(!cssProperties.isKnown("--foo bar"),
       "A CSS variable with spaces fails");
 
-    is(toSortedString(cssProperties.getValues('margin')),
-       toSortedString(["auto","calc","inherit","initial","unset"]),
+    is(toSortedString(cssProperties.getValues("margin")),
+       toSortedString(["auto", "calc", "inherit", "initial", "unset"]),
        "Can get values for the CSS margin.");
-    is(cssProperties.getValues('foobar').length, 0,
+    is(cssProperties.getValues("foobar").length, 0,
       "Unknown values return an empty array.");
 
-    const bgColorValues = cssProperties.getValues('background-color');
+    const bgColorValues = cssProperties.getValues("background-color");
     ok(bgColorValues.includes("blanchedalmond"),
       "A property with color values includes blanchedalmond.");
     ok(bgColorValues.includes("papayawhip"),
@@ -111,7 +113,7 @@ window.onload = function() {
 
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_device.html b/devtools/server/tests/mochitest/test_device.html
index e739fa5fc2d2..f126b7603941 100644
--- a/devtools/server/tests/mochitest/test_device.html
+++ b/devtools/server/tests/mochitest/test_device.html
@@ -12,37 +12,38 @@ Bug 895360 - [app manager] Device meta data actor
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
-  var Cu = Components.utils;
-  var Cc = Components.classes;
-  var Ci = Components.interfaces;
+window.onload = function () {
+  const Cu = Components.utils;
+  const Cc = Components.classes;
+  const Ci = Components.interfaces;
 
-  var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-  var {DebuggerClient} = require("devtools/shared/client/main");
-  var {DebuggerServer} = require("devtools/server/main");
-  var Services = require("Services");
+  const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
+  const {DebuggerClient} = require("devtools/shared/client/main");
+  const {DebuggerServer} = require("devtools/server/main");
+  const Services = require("Services");
 
   SimpleTest.waitForExplicitFinish();
 
-  var {getDeviceFront} = require("devtools/shared/fronts/device");
+  const {getDeviceFront} = require("devtools/shared/fronts/device");
 
   if (!DebuggerServer.initialized) {
     DebuggerServer.init();
     DebuggerServer.addBrowserActors();
   }
 
-  var client = new DebuggerClient(DebuggerServer.connectPipe());
+  let client = new DebuggerClient(DebuggerServer.connectPipe());
   client.connect().then(function onConnect() {
-    client.listTabs(function onListTabs(aResponse) {
-      var d = getDeviceFront(client, aResponse);
+    client.listTabs(function onListTabs(response) {
+      let d = getDeviceFront(client, response);
 
-      var desc;
-      var appInfo = Services.appinfo;
-      var utils = window.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+      let desc;
+      let appInfo = Services.appinfo;
+      let utils = window.QueryInterface(Ci.nsIInterfaceRequestor)
+                        .getInterface(Ci.nsIDOMWindowUtils);
 
-
-      var localDesc = {
+      let localDesc = {
         appid: appInfo.ID,
         vendor: appInfo.vendor,
         name: appInfo.name,
@@ -53,38 +54,38 @@ window.onload = function() {
         geckobuildid: appInfo.platformBuildID,
         geckoversion: appInfo.platformVersion,
         useragent: window.navigator.userAgent,
-        locale: Cc["@mozilla.org/chrome/chrome-registry;1"].getService(Ci.nsIXULChromeRegistry).getSelectedLocale("global"),
+        locale: Cc["@mozilla.org/chrome/chrome-registry;1"]
+                .getService(Ci.nsIXULChromeRegistry).getSelectedLocale("global"),
         os: appInfo.OS,
         processor: appInfo.XPCOMABI.split("-")[0],
         compiler: appInfo.XPCOMABI.split("-")[1],
         dpi: utils.displayDPI,
         width: window.screen.width,
         height: window.screen.height
-      }
+      };
 
       function checkValues() {
-        for (var key in localDesc) {
+        for (let key in localDesc) {
           is(desc[key], localDesc[key], "valid field (" + key + ")");
         }
 
-        var currProfD = Services.dirsvc.get("ProfD", Ci.nsIFile);
-        var profileDir = currProfD.path;
-        ok(profileDir.indexOf(desc.profile.length > 0 && desc.profile) != -1, "valid profile name");
+        let currProfD = Services.dirsvc.get("ProfD", Ci.nsIFile);
+        let profileDir = currProfD.path;
+        ok(profileDir.indexOf(desc.profile.length > 0 && desc.profile) != -1,
+           "valid profile name");
 
         client.close().then(() => {
           DebuggerServer.destroy();
-          SimpleTest.finish()
+          SimpleTest.finish();
         });
       }
 
-
-      d.getDescription().then((v) => desc = v)
-      .then(checkValues);
-
+      d.getDescription().then(function (v) {
+        desc = v;
+      }).then(checkValues);
     });
   });
-
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_director.html b/devtools/server/tests/mochitest/test_director.html
index 37aebad12593..74107597ac5a 100644
--- a/devtools/server/tests/mochitest/test_director.html
+++ b/devtools/server/tests/mochitest/test_director.html
@@ -14,43 +14,45 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
 <pre id="test">
   <script type="application/javascript" src="./director-helpers.js"></script>
   <script type="application/javascript">
-const WAIT_EVENT_TIMEOUT = 3000;
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   Task.spawn(function* () {
     SimpleTest.waitForExplicitFinish();
 
-    var tests = [
+    let tests = [
       runDirectorRegistryActorTest
     ].map((testCase) => {
       return function* () {
         setup();
         yield testCase().then(null, (e) => {
           console.error("Exception during testCase run", e);
-          ok(false, "Exception during testCase run: " + [e, e.fileName, e.lineNumber].join("\n\t"));
+          ok(false, "Exception during testCase run: "
+                    + [e, e.fileName, e.lineNumber].join("\n\t"));
         });
 
         teardown();
       };
     });
 
-    for (var test of tests) {
+    for (let test of tests) {
       yield test();
     }
   }).then(
     function success() {
-      SimpleTest.finish()
+      SimpleTest.finish();
     },
     function error(e) {
       console.error("Exception during testCase run", e);
-      ok(false, "Exception during testCase run: " + [e, e.fileName, e.lineNumber].join("\n\t"));
+      ok(false, "Exception during testCase run: "
+                + [e, e.fileName, e.lineNumber].join("\n\t"));
 
       SimpleTest.finish();
     }
   );
 };
 
-var targetWin = null;
+let targetWin = null;
 
 function setup() {
   if (!DebuggerServer.initialized) {
@@ -70,30 +72,26 @@ function teardown() {
   }
 }
 
-/***********************************
- *  test cases
- **********************************/
-
-
 function runDirectorRegistryActorTest() {
   let testDirectorScriptOptions = {
-    scriptCode: "(" + (function() {
-      module.exports = function({port}) {
-        port.onmessage = function(evt) {
+    scriptCode: "(" + (function () {
+      module.exports = function ({port}) {
+        port.onmessage = function (evt) {
           // echo messages
           evt.target.postMessage(evt.data);
         };
       };
     }).toString() + ")();",
     scriptOptions: {}
-  }
+  };
 
   return Task.spawn(function* () {
     let { client, root } = yield newConnectedDebuggerClient();
 
-    var directorRegistryClient = new DirectorRegistryFront(client, root);
+    let directorRegistryClient = new DirectorRegistryFront(client, root);
 
-    let installed = yield directorRegistryClient.install("testDirectorScript", testDirectorScriptOptions);
+    let installed = yield directorRegistryClient.install("testDirectorScript",
+                                                         testDirectorScriptOptions);
     is(installed, true, "DirectorManager.install returns true");
 
     let list = yield directorRegistryClient.list();
@@ -106,8 +104,6 @@ function runDirectorRegistryActorTest() {
     yield client.close();
   });
 }
-
-
   </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_director_connectToChild.html b/devtools/server/tests/mochitest/test_director_connectToChild.html
index 55335e8ffb6c..fa562bc885b0 100644
--- a/devtools/server/tests/mochitest/test_director_connectToChild.html
+++ b/devtools/server/tests/mochitest/test_director_connectToChild.html
@@ -14,24 +14,27 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
 <pre id="test">
   <script type="application/javascript" src="./director-helpers.js"></script>
   <script type="application/javascript">
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   Task.spawn(function* () {
     SimpleTest.waitForExplicitFinish();
 
-    var tests = [
+    let tests = [
       runPropagateDirectorScriptsToChildTest,
     ].map((testCase) => {
       return function* () {
         setup();
         yield testCase().then(null, (e) => {
-          ok(false, "Exception during testCase run: " + [e, e.fileName, e.lineNumber].join("\n\t"));
+          ok(false, "Exception during testCase run: "
+                    + [e, e.fileName, e.lineNumber].join("\n\t"));
         });
 
         teardown();
       };
     });
 
-    for (var test of tests) {
+    for (let test of tests) {
       yield test();
     }
 
@@ -43,7 +46,7 @@ function setup() {
   if (!DebuggerServer.initialized) {
     DebuggerServer.init(() => true);
     DebuggerServer.addBrowserActors();
-    SimpleTest.registerCleanupFunction(function() {
+    SimpleTest.registerCleanupFunction(function () {
       DebuggerServer.destroy();
     });
   }
@@ -54,10 +57,6 @@ function teardown() {
   DebuggerServer.destroy();
 }
 
-/***********************************
- *  test cases
- **********************************/
-
 function runPropagateDirectorScriptsToChildTest() {
   let iframe = document.createElement("iframe");
   iframe.mozbrowser = true;
@@ -65,9 +64,9 @@ function runPropagateDirectorScriptsToChildTest() {
   document.body.appendChild(iframe);
 
   return Task.spawn(function* () {
-    var { client, root, transport } = yield newConnectedDebuggerClient();
+    let { client, root, transport } = yield newConnectedDebuggerClient();
 
-    var directorRegistryClient = new DirectorRegistryFront(client, root);
+    let directorRegistryClient = new DirectorRegistryFront(client, root);
 
     // install a director script
     yield directorRegistryClient.install("testPropagatedDirectorScript", {
@@ -75,19 +74,19 @@ function runPropagateDirectorScriptsToChildTest() {
       scriptOptions: {}
     });
 
-    var conn = transport._serverConnection;
-    var childActor = yield DebuggerServer.connectToChild(conn, iframe);
+    let conn = transport._serverConnection;
+    let childActor = yield DebuggerServer.connectToChild(conn, iframe);
 
     ok(typeof childActor.directorManagerActor !== "undefined",
        "childActor.directorActor should be defined");
 
-    var childDirectorManagerClient = new DirectorManagerFront(client, childActor);
+    let childDirectorManagerClient = new DirectorManagerFront(client, childActor);
 
-    var directorScriptList = yield childDirectorManagerClient.list();
+    let directorScriptList = yield childDirectorManagerClient.list();
 
     ok(directorScriptList.installed.length === 1 &&
        directorScriptList.installed[0] === "testPropagatedDirectorScript",
-       "director scripts propagated correctly")
+       "director scripts propagated correctly");
 
     yield client.close();
   });
diff --git a/devtools/server/tests/mochitest/test_executeInGlobal-outerized_this.html b/devtools/server/tests/mochitest/test_executeInGlobal-outerized_this.html
index 8bedde618f1f..86bd27e236c9 100644
--- a/devtools/server/tests/mochitest/test_executeInGlobal-outerized_this.html
+++ b/devtools/server/tests/mochitest/test_executeInGlobal-outerized_this.html
@@ -16,6 +16,7 @@ object.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 Components.utils.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
@@ -23,46 +24,49 @@ addDebuggerToGlobal(this);
 window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var iframe = document.createElement("iframe");
+  let iframe = document.createElement("iframe");
   iframe.src = "data:text/html,<script>var me = 'page 1';<\/script>";
   iframe.onload = firstOnLoadHandler;
   document.body.appendChild(iframe);
 
   function firstOnLoadHandler() {
-    var dbg = new Debugger;
-    var page1DO = dbg.addDebuggee(iframe.contentWindow);
+    let dbg = new Debugger();
+    let page1DO = dbg.addDebuggee(iframe.contentWindow);
     iframe.src = "data:text/html,<script>var me = 'page 2';<\/script>";
     iframe.onload = function () {
-      var page2DO = dbg.addDebuggee(iframe.contentWindow);
+      let page2DO = dbg.addDebuggee(iframe.contentWindow);
       ok(page1DO !== page2DO, "the two pages' globals get distinct D.O's");
       ok(page1DO.unsafeDereference() === page2DO.unsafeDereference(),
          "unwrapping page1DO and page2DO outerizes both, yielding the same outer window");
 
-      is(page1DO.executeInGlobal('me').return, 'page 1', "page1DO continues to refer to original page");
-      is(page2DO.executeInGlobal('me').return, 'page 2', "page2DO refers to current page");
+      is(page1DO.executeInGlobal("me").return,
+         "page 1", "page1DO continues to refer to original page");
+      is(page2DO.executeInGlobal("me").return, "page 2",
+         "page2DO refers to current page");
 
-      is(page1DO.executeInGlobal('this === window').return, true,
+      is(page1DO.executeInGlobal("this === window").return, true,
          "page 1: Debugger.Object.prototype.executeInGlobal should outerize 'this'");
-      is(page1DO.executeInGlobalWithBindings('this === window', {x:2}).return, true,
+      is(page1DO.executeInGlobalWithBindings("this === window", {x: 2}).return, true,
          "page 1: Debugger.Object.prototype.executeInGlobal should outerize 'this'");
 
-      is(page2DO.executeInGlobal('this === window').return, true,
+      is(page2DO.executeInGlobal("this === window").return, true,
          "page 2: Debugger.Object.prototype.executeInGlobal should outerize 'this'");
-      is(page2DO.executeInGlobalWithBindings('this === window', {x:2}).return, true,
+      is(page2DO.executeInGlobalWithBindings("this === window", {x: 2}).return, true,
          "page 2: Debugger.Object.prototype.executeInGlobal should outerize 'this'");
 
       // Debugger doesn't let one use outer windows as globals. You have to innerize.
-      var outerDO = page1DO.makeDebuggeeValue(page1DO.unsafeDereference());
-      ok(outerDO !== page1DO, "outer window gets its own D.O, distinct from page 1's global");
-      ok(outerDO !== page2DO, "outer window gets its own D.O, distinct from page 2's global");
-      SimpleTest.doesThrow(function () { outerDO.executeInGlobal('me'); },
+      let outerDO = page1DO.makeDebuggeeValue(page1DO.unsafeDereference());
+      ok(outerDO !== page1DO,
+         "outer window gets its own D.O, distinct from page 1's global");
+      ok(outerDO !== page2DO,
+         "outer window gets its own D.O, distinct from page 2's global");
+      SimpleTest.doesThrow(() => outerDO.executeInGlobal("me"),
                            "outer window D.Os can't be used as globals");
 
       SimpleTest.finish();
-    }
+    };
   }
-}
-
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_framerate_01.html b/devtools/server/tests/mochitest/test_framerate_01.html
index 0282d50a267b..5fba97ca52cf 100644
--- a/devtools/server/tests/mochitest/test_framerate_01.html
+++ b/devtools/server/tests/mochitest/test_framerate_01.html
@@ -12,30 +12,29 @@ Bug 1007200 - Create a framerate actor
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
-  var Cu = Components.utils;
-  var Cc = Components.classes;
-  var Ci = Components.interfaces;
+window.onload = function () {
+  const Cu = Components.utils;
 
-  var { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
-  var Services = require("Services");
-  var { DebuggerClient } = require("devtools/shared/client/main");
-  var { DebuggerServer } = require("devtools/server/main");
+  const { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
+  const Services = require("Services");
+  const { DebuggerClient } = require("devtools/shared/client/main");
+  const { DebuggerServer } = require("devtools/server/main");
 
   // Always log packets when running tests.
   Services.prefs.setBoolPref("devtools.debugger.log", true);
-  SimpleTest.registerCleanupFunction(function() {
+  SimpleTest.registerCleanupFunction(function () {
     Services.prefs.clearUserPref("devtools.debugger.log");
   });
 
   SimpleTest.waitForExplicitFinish();
 
-  var {FramerateFront} = require("devtools/shared/fronts/framerate");
+  const { FramerateFront } = require("devtools/shared/fronts/framerate");
 
   function plotFPS(ticks, interval = 100, clamp = 60) {
-    var timeline = [];
-    var totalTicks = ticks.length;
+    let timeline = [];
+    let totalTicks = ticks.length;
 
     // If the refresh driver didn't get a chance to tick before the
     // recording was stopped, assume framerate was 0.
@@ -45,19 +44,19 @@ window.onload = function() {
       return timeline;
     }
 
-    var frameCount = 0;
-    var prevTime = ticks[0];
+    let frameCount = 0;
+    let prevTime = ticks[0];
 
-    for (var i = 1; i < totalTicks; i++) {
-      var currTime = ticks[i];
+    for (let i = 1; i < totalTicks; i++) {
+      let currTime = ticks[i];
       frameCount++;
 
-      var elapsedTime = currTime - prevTime;
+      let elapsedTime = currTime - prevTime;
       if (elapsedTime < interval) {
         continue;
       }
 
-      var framerate = Math.min(1000 / (elapsedTime / frameCount), clamp);
+      let framerate = Math.min(1000 / (elapsedTime / frameCount), clamp);
       timeline.push({ delta: prevTime, value: framerate });
       timeline.push({ delta: currTime, value: framerate });
 
@@ -66,20 +65,21 @@ window.onload = function() {
     }
 
     return timeline;
-  };
+  }
 
   if (!DebuggerServer.initialized) {
     DebuggerServer.init();
     DebuggerServer.addBrowserActors();
   }
 
-  var client = new DebuggerClient(DebuggerServer.connectPipe());
+  let client = new DebuggerClient(DebuggerServer.connectPipe());
   client.connect().then(function onConnect() {
-    client.listTabs(function onListTabs(aResponse) {
-      var form = aResponse.tabs[aResponse.selected];
-      var front = FramerateFront(client, form);
+    client.listTabs(function onListTabs(response) {
+      let form = response.tabs[response.selected];
+      let front = FramerateFront(client, form);
 
       window.setTimeout(() => {
+        /* eslint-disable max-nested-callbacks */
         front.startRecording().then(() => {
           window.setTimeout(() => {
             front.stopRecording().then(rawData => {
@@ -87,6 +87,7 @@ window.onload = function() {
             });
           }, 1000);
         });
+        /* eslint-enable max-nested-callbacks */
       }, 1000);
     });
   });
@@ -94,15 +95,15 @@ window.onload = function() {
   function onRecordingStopped(front, rawData) {
     ok(rawData, "There should be a recording available.");
 
-    var timeline = plotFPS(rawData);
+    let timeline = plotFPS(rawData);
     ok(timeline.length >= 2,
       "There should be at least one measurement available, with two entries.");
 
-    var prevTimeStart = timeline[0].delta;
+    let prevTimeStart = timeline[0].delta;
 
-    for (var i = 0; i < timeline.length; i += 2) {
-      var currTimeStart = timeline[i].delta;
-      var currTimeEnd = timeline[i + 1].delta;
+    for (let i = 0; i < timeline.length; i += 2) {
+      let currTimeStart = timeline[i].delta;
+      let currTimeEnd = timeline[i + 1].delta;
       info("Testing delta: " + currTimeStart + " vs. " + currTimeEnd);
 
       ok(currTimeStart < currTimeEnd,
@@ -113,28 +114,24 @@ window.onload = function() {
       prevTimeStart = currTimeEnd;
     }
 
-    var prevFramerateValue = -1;
-
-    for (var i = 0; i < timeline.length; i += 2) {
-      var currFramerateStart = timeline[i].value;
-      var currFramerateEnd = timeline[i + 1].value;
+    for (let i = 0; i < timeline.length; i += 2) {
+      let currFramerateStart = timeline[i].value;
+      let currFramerateEnd = timeline[i + 1].value;
       info("Testing framerate: " + currFramerateStart);
 
       is(currFramerateStart, currFramerateEnd,
         "The start and end framerate values should be equal.");
 
       is(typeof currFramerateStart, "number", "All values should be numbers.");
-      ok(currFramerateStart <= 60, "All values were correctly clamped.")
-
-      prevFramerateValue = currFramerateStart;
+      ok(currFramerateStart <= 60, "All values were correctly clamped.");
     }
 
     client.close().then(() => {
       DebuggerServer.destroy();
-      SimpleTest.finish()
+      SimpleTest.finish();
     });
   }
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_framerate_02.html b/devtools/server/tests/mochitest/test_framerate_02.html
index 9d4626b126a1..295e640fbccd 100644
--- a/devtools/server/tests/mochitest/test_framerate_02.html
+++ b/devtools/server/tests/mochitest/test_framerate_02.html
@@ -12,30 +12,29 @@ Bug 1007200 - Create a framerate actor
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
-  var Cu = Components.utils;
-  var Cc = Components.classes;
-  var Ci = Components.interfaces;
+window.onload = function () {
+  const Cu = Components.utils;
 
-  var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-  var {DebuggerClient} = require("devtools/shared/client/main");
-  var {DebuggerServer} = require("devtools/server/main");
-  var Services = require("Services");
+  const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
+  const {DebuggerClient} = require("devtools/shared/client/main");
+  const {DebuggerServer} = require("devtools/server/main");
+  const Services = require("Services");
 
   // Always log packets when running tests.
   Services.prefs.setBoolPref("devtools.debugger.log", true);
-  SimpleTest.registerCleanupFunction(function() {
+  SimpleTest.registerCleanupFunction(function () {
     Services.prefs.clearUserPref("devtools.debugger.log");
   });
 
   SimpleTest.waitForExplicitFinish();
 
-  var {FramerateFront} = require("devtools/shared/fronts/framerate");
+  const {FramerateFront} = require("devtools/shared/fronts/framerate");
 
   function plotFPS(ticks, interval = 100, clamp = 60) {
-    var timeline = [];
-    var totalTicks = ticks.length;
+    let timeline = [];
+    let totalTicks = ticks.length;
 
     // If the refresh driver didn't get a chance to tick before the
     // recording was stopped, assume framerate was 0.
@@ -45,19 +44,19 @@ window.onload = function() {
       return timeline;
     }
 
-    var frameCount = 0;
-    var prevTime = ticks[0];
+    let frameCount = 0;
+    let prevTime = ticks[0];
 
-    for (var i = 1; i < totalTicks; i++) {
-      var currTime = ticks[i];
+    for (let i = 1; i < totalTicks; i++) {
+      let currTime = ticks[i];
       frameCount++;
 
-      var elapsedTime = currTime - prevTime;
+      let elapsedTime = currTime - prevTime;
       if (elapsedTime < interval) {
         continue;
       }
 
-      var framerate = Math.min(1000 / (elapsedTime / frameCount), clamp);
+      let framerate = Math.min(1000 / (elapsedTime / frameCount), clamp);
       timeline.push({ delta: prevTime, value: framerate });
       timeline.push({ delta: currTime, value: framerate });
 
@@ -66,24 +65,24 @@ window.onload = function() {
     }
 
     return timeline;
-  };
+  }
 
   if (!DebuggerServer.initialized) {
     DebuggerServer.init();
     DebuggerServer.addBrowserActors();
   }
 
-  var client = new DebuggerClient(DebuggerServer.connectPipe());
+  let client = new DebuggerClient(DebuggerServer.connectPipe());
   client.connect().then(function onConnect() {
-    client.listTabs(function onListTabs(aResponse) {
-      var form = aResponse.tabs[aResponse.selected];
-      var front = FramerateFront(client, form);
+    client.listTabs(function onListTabs(response) {
+      let form = response.tabs[response.selected];
+      let front = FramerateFront(client, form);
 
       front.stopRecording().then(rawData => {
         ok(rawData, "There should be a recording available.");
         is(rawData.length, 0, "...but it should be empty.");
 
-        var timeline = plotFPS(rawData);
+        let timeline = plotFPS(rawData);
         is(timeline.length, 2,
           "There should be one measurement plotted, with two entries.");
 
@@ -99,14 +98,15 @@ window.onload = function() {
         is(timeline[1].value, 0,
           "The last framerate value should be 0.");
 
+        // eslint-disable-next-line max-nested-callbacks
         client.close().then(() => {
           DebuggerServer.destroy();
-          SimpleTest.finish()
+          SimpleTest.finish();
         });
       });
     });
   });
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_framerate_03.html b/devtools/server/tests/mochitest/test_framerate_03.html
index da76ebc2061b..88d6b1c8355a 100644
--- a/devtools/server/tests/mochitest/test_framerate_03.html
+++ b/devtools/server/tests/mochitest/test_framerate_03.html
@@ -12,47 +12,48 @@ Bug 1023018 - Tests whether or not the framerate actor can handle time ranges.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
-  var Cu = Components.utils;
-  var Cc = Components.classes;
-  var Ci = Components.interfaces;
+window.onload = function () {
+  const Cu = Components.utils;
 
-  var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-  var {DebuggerClient} = require("devtools/shared/client/main");
-  var {DebuggerServer} = require("devtools/server/main");
-  var Services = require("Services");
+  const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
+  const {DebuggerClient} = require("devtools/shared/client/main");
+  const {DebuggerServer} = require("devtools/server/main");
+  const Services = require("Services");
 
   // Always log packets when running tests.
   Services.prefs.setBoolPref("devtools.debugger.log", true);
-  SimpleTest.registerCleanupFunction(function() {
+  SimpleTest.registerCleanupFunction(function () {
     Services.prefs.clearUserPref("devtools.debugger.log");
   });
 
   SimpleTest.waitForExplicitFinish();
 
-  var {FramerateFront} = require("devtools/shared/fronts/framerate");
-  var START_TICK = 2000;
-  var STOP_TICK = 3000;
-  var TOTAL_TIME = 5000;
+  const {FramerateFront} = require("devtools/shared/fronts/framerate");
+  const START_TICK = 2000;
+  const STOP_TICK = 3000;
+  const TOTAL_TIME = 5000;
 
   if (!DebuggerServer.initialized) {
     DebuggerServer.init();
     DebuggerServer.addBrowserActors();
   }
 
-  var client = new DebuggerClient(DebuggerServer.connectPipe());
+  let client = new DebuggerClient(DebuggerServer.connectPipe());
   client.connect().then(function onConnect() {
-    client.listTabs(function onListTabs(aResponse) {
-      var form = aResponse.tabs[aResponse.selected];
-      var front = FramerateFront(client, form);
+    client.listTabs(function onListTabs(response) {
+      let form = response.tabs[response.selected];
+      let front = FramerateFront(client, form);
 
       front.startRecording().then(() => {
+        /* eslint-disable max-nested-callbacks */
         window.setTimeout(() => {
           front.stopRecording(START_TICK, STOP_TICK).then(rawData => {
             onRecordingStopped(front, rawData);
           });
         }, TOTAL_TIME);
+        /* eslint-enable max-nested-callbacks */
       });
     });
   });
@@ -65,17 +66,17 @@ window.onload = function() {
     ok(!rawData.find(e => e > STOP_TICK),
       "There should be no tick after 3000ms.");
 
-    for (var tick of rawData) {
+    for (let tick of rawData) {
       info("Testing tick: " + tick);
       is(typeof tick, "number", "All values should be numbers.");
     }
 
     client.close().then(() => {
       DebuggerServer.destroy();
-      SimpleTest.finish()
+      SimpleTest.finish();
     });
   }
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_framerate_04.html b/devtools/server/tests/mochitest/test_framerate_04.html
index 7617ddfb7320..328d78143040 100644
--- a/devtools/server/tests/mochitest/test_framerate_04.html
+++ b/devtools/server/tests/mochitest/test_framerate_04.html
@@ -13,26 +13,28 @@ Bug 1023018 - Tests if the framerate actor keeps recording after navigations.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
-  var {FramerateFront} = require("devtools/shared/fronts/framerate");
-  var {TargetFactory} = require("devtools/client/framework/target");
+  const {FramerateFront} = require("devtools/shared/fronts/framerate");
+  const {TargetFactory} = require("devtools/client/framework/target");
 
-  var url = document.getElementById("testContent").href;
+  let url = document.getElementById("testContent").href;
   attachURL(url, onTab);
 
   function onTab(_, client, form, contentDoc) {
-    var contentWin = contentDoc.defaultView;
-    var chromeWin = Services.wm.getMostRecentWindow("navigator:browser");
-    var selectedTab = chromeWin.gBrowser.selectedTab;
+    let contentWin = contentDoc.defaultView;
+    let chromeWin = Services.wm.getMostRecentWindow("navigator:browser");
+    let selectedTab = chromeWin.gBrowser.selectedTab;
 
-    var target = TargetFactory.forTab(selectedTab);
-    var front = FramerateFront(client, form);
+    let target = TargetFactory.forTab(selectedTab);
+    let front = FramerateFront(client, form);
 
     front.startRecording().then(() => {
       window.setTimeout(() => {
         front.getPendingTicks().then(firstBatch => {
+          /* eslint-disable max-nested-callbacks */
           target.once("will-navigate", () => {
             window.setTimeout(() => {
               front.stopRecording().then(secondBatch => {
@@ -40,6 +42,7 @@ window.onload = function() {
               });
             }, 1000);
           });
+          /* eslint-enable max-nested-callbacks */
           contentWin.location.reload();
         });
       }, 1000);
@@ -50,7 +53,7 @@ window.onload = function() {
     ok(firstBatch, "There should be a first batch recording available.");
     ok(secondBatch, "There should be a second batch recording available.");
 
-    var diff = secondBatch.length - firstBatch.length;
+    let diff = secondBatch.length - firstBatch.length;
     info("Difference in ticks: " + diff);
     ok(diff > 0, "More ticks should be recorded in the second batch.");
 
@@ -61,10 +64,10 @@ window.onload = function() {
 
     client.close().then(() => {
       DebuggerServer.destroy();
-      SimpleTest.finish()
+      SimpleTest.finish();
     });
   }
-}
+};
 </script>
 </pre>
 <a id="testContent" target="_blank" href="inspector_getImageData.html">Test Document</a>
diff --git a/devtools/server/tests/mochitest/test_framerate_05.html b/devtools/server/tests/mochitest/test_framerate_05.html
index 96f56a18fcca..f5c36537761b 100644
--- a/devtools/server/tests/mochitest/test_framerate_05.html
+++ b/devtools/server/tests/mochitest/test_framerate_05.html
@@ -12,37 +12,37 @@ Bug 1034648 - Tests whether a framerate recording can be cancelled.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
-  var Cu = Components.utils;
-  var Cc = Components.classes;
-  var Ci = Components.interfaces;
+window.onload = function () {
+  let Cu = Components.utils;
 
-  var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-  var {DebuggerClient} = require("devtools/shared/client/main");
-  var {DebuggerServer} = require("devtools/server/main");
-  var Services = require("Services");
+  const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
+  const {DebuggerClient} = require("devtools/shared/client/main");
+  const {DebuggerServer} = require("devtools/server/main");
+  const Services = require("Services");
 
   // Always log packets when running tests.
   Services.prefs.setBoolPref("devtools.debugger.log", true);
-  SimpleTest.registerCleanupFunction(function() {
+  SimpleTest.registerCleanupFunction(function () {
     Services.prefs.clearUserPref("devtools.debugger.log");
   });
 
   SimpleTest.waitForExplicitFinish();
 
-  var {FramerateFront} = require("devtools/shared/fronts/framerate");
+  const {FramerateFront} = require("devtools/shared/fronts/framerate");
 
   DebuggerServer.init();
   DebuggerServer.addBrowserActors();
 
-  var client = new DebuggerClient(DebuggerServer.connectPipe());
+  let client = new DebuggerClient(DebuggerServer.connectPipe());
   client.connect().then(function onConnect() {
-    client.listTabs(function onListTabs(aResponse) {
-      var form = aResponse.tabs[aResponse.selected];
-      var front = FramerateFront(client, form);
+    client.listTabs(function onListTabs(response) {
+      let form = response.tabs[response.selected];
+      let front = FramerateFront(client, form);
 
       front.startRecording().then(() => {
+        /* eslint-disable max-nested-callbacks */
         window.setTimeout(() => {
           front.cancelRecording().then(() => {
             window.setTimeout(() => {
@@ -60,17 +60,18 @@ window.onload = function() {
 
                   client.close().then(() => {
                     DebuggerServer.destroy();
-                    SimpleTest.finish()
+                    SimpleTest.finish();
                   });
                 });
               });
             }, 1000);
           });
         }, 1000);
+        /* eslint-enable max-nested-callbacks */
       });
     });
   });
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_framerate_06.html b/devtools/server/tests/mochitest/test_framerate_06.html
index 32be07a92f4a..b97aade97ef1 100644
--- a/devtools/server/tests/mochitest/test_framerate_06.html
+++ b/devtools/server/tests/mochitest/test_framerate_06.html
@@ -13,34 +13,33 @@ Bug 1171489 - Tests if the framerate actor does not record timestamps from multi
 <body>
 <pre id="test">
 <script>
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
-  var {FramerateFront} = require("devtools/shared/fronts/framerate");
-  var {TargetFactory} = require("devtools/client/framework/target");
+  const {FramerateFront} = require("devtools/shared/fronts/framerate");
 
-  var url = document.getElementById("testContent").href;
+  let url = document.getElementById("testContent").href;
   attachURL(url, onTab);
 
   function onTab(_, client, form, contentDoc) {
-    var contentWin = contentDoc.defaultView;
-    var chromeWin = Services.wm.getMostRecentWindow("navigator:browser");
-    var selectedTab = chromeWin.gBrowser.selectedTab;
+    let contentWin = contentDoc.defaultView;
 
-    var target = TargetFactory.forTab(selectedTab);
-    var front = FramerateFront(client, form);
+    let front = FramerateFront(client, form);
 
     front.startRecording().then(() => {
       window.setTimeout(() => {
         // Wait for the iframe to be loaded again
-        window.addEventListener("message", function loaded (event) {
+        window.addEventListener("message", function loaded(event) {
           if (event.data === "ready") {
             window.removeEventListener("message", loaded);
+            /* eslint-disable max-nested-callbacks */
             window.setTimeout(() => {
               front.stopRecording().then(ticks => {
                 onRecordingStopped(client, ticks);
               });
             }, 1000);
+            /* eslint-enable max-nested-callbacks */
           }
         });
         contentWin.location.reload();
@@ -49,13 +48,13 @@ window.onload = function() {
   }
 
   function onRecordingStopped(client, ticks) {
-    var diffs = [];
+    let diffs = [];
 
     info(`Got ${ticks.length} ticks.`);
 
-    for (var i = 1; i < ticks.length; i++) {
-      var prev = ticks[i - 1];
-      var curr = ticks[i];
+    for (let i = 1; i < ticks.length; i++) {
+      let prev = ticks[i - 1];
+      let curr = ticks[i];
       diffs.push(curr - prev);
       info(curr + " - " + (curr - prev));
     }
@@ -64,17 +63,19 @@ window.onload = function() {
     // when we get ticks from other frames they're usually at diffs of < 1. Sometimes
     // ticks can still be less than 16ms even on one frame (usually following a very slow
     // frame), so use a low number (2) to be our threshold
-    var THRESHOLD = 2;
-    ok(ticks.length >= 20, "we should have atleast 20 ticks over the course of two seconds.");
-    var belowThreshold = diffs.filter(v => v <= THRESHOLD);
-    ok(belowThreshold.length <= 10, "we should have very few frames less than the threshold");
+    let THRESHOLD = 2;
+    ok(ticks.length >= 20,
+       "we should have atleast 20 ticks over the course of two seconds.");
+    let belowThreshold = diffs.filter(v => v <= THRESHOLD);
+    ok(belowThreshold.length <= 10,
+       "we should have very few frames less than the threshold");
 
     client.close().then(() => {
       DebuggerServer.destroy();
-      SimpleTest.finish()
+      SimpleTest.finish();
     });
   }
-}
+};
 </script>
 </pre>
 <a id="testContent" target="_blank" href="inspector-traversal-data.html">Test Document</a>
diff --git a/devtools/server/tests/mochitest/test_getProcess.html b/devtools/server/tests/mochitest/test_getProcess.html
index c29a07ee6943..f891ea96fb6b 100644
--- a/devtools/server/tests/mochitest/test_getProcess.html
+++ b/devtools/server/tests/mochitest/test_getProcess.html
@@ -12,17 +12,16 @@ Bug 1060093 - Test DebuggerServer.getProcess
 <body>
 <pre id="test">
 <script type="application/javascript">
+"use strict";
 
 let Cu = Components.utils;
-let Cc = Components.classes;
-let Ci = Components.interfaces;
 
 let {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
 let {DebuggerClient} = require("devtools/shared/client/main");
 let {DebuggerServer} = require("devtools/server/main");
 let Services = require("Services");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   SpecialPowers.pushPrefEnv({
@@ -35,7 +34,7 @@ window.onload = function() {
       ["dom.ipc.processCount", 10],
     ]
   }, runTests);
-}
+};
 
 function runTests() {
   // Instantiate a minimal server
@@ -81,13 +80,13 @@ function runTests() {
   function getProcess() {
     client.mainRoot.listProcesses(response => {
       ok(response.processes.length >= 2, "Got at least the parent process and one child");
-      is(response.processes.length, processCount+1 , "Got one additional process on the second call to listProcesses");
+      is(response.processes.length, processCount + 1,
+         "Got one additional process on the second call to listProcesses");
 
       // Connect to the first content processe available
       let content = response.processes.filter(p => (!p.parent))[0];
 
-      client.getProcess(content.id).then(response => {
-        let actor = response.form;
+      client.getProcess(content.id).then(({form: actor}) => {
         ok(actor.consoleActor, "Got the console actor");
         ok(actor.chromeDebugger, "Got the thread actor");
 
@@ -96,8 +95,8 @@ function runTests() {
           to: actor.consoleActor,
           type: "evaluateJS",
           text: "var a = 42; a"
-        }, function (response) {
-          ok(response.result, 42, "console.eval worked");
+        }, function ({result}) {
+          ok(result, 42, "console.eval worked");
 
           getProcessAgain(actor, content.id);
         });
@@ -118,7 +117,7 @@ function runTests() {
 
   function processScript() {
     let listener = function () {
-      Services.obs.removeObserver(listener, "sdk:loader:destroy", false);
+      Services.obs.removeObserver(listener, "sdk:loader:destroy");
       sendAsyncMessage("test:getProcess-destroy", null);
     };
     Services.obs.addObserver(listener, "sdk:loader:destroy", false);
@@ -127,10 +126,10 @@ function runTests() {
   function closeClient() {
     let onLoaderDestroyed = new Promise(done => {
       let processListener = function () {
-        Services.ppmm.removeMessageListener("test:getProcess-destroy", processListener)
+        Services.ppmm.removeMessageListener("test:getProcess-destroy", processListener);
         done();
       };
-      Services.ppmm.addMessageListener("test:getProcess-destroy", processListener)
+      Services.ppmm.addMessageListener("test:getProcess-destroy", processListener);
     });
     let script = "data:,(" + processScript + ")()";
     Services.ppmm.loadProcessScript(script, true);
@@ -147,7 +146,7 @@ function runTests() {
   function cleanup() {
     DebuggerServer.destroy();
     iframe.remove();
-    SimpleTest.finish()
+    SimpleTest.finish();
   }
 
   connect();
diff --git a/devtools/server/tests/mochitest/test_inspector-anonymous.html b/devtools/server/tests/mochitest/test_inspector-anonymous.html
index 864e3ce8a272..3f5147b1f0a9 100644
--- a/devtools/server/tests/mochitest/test_inspector-anonymous.html
+++ b/devtools/server/tests/mochitest/test_inspector-anonymous.html
@@ -11,7 +11,9 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=777674
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   const {InspectorFront} =
     require("devtools/shared/fronts/inspector");
   const {_documentWalker} =
@@ -26,51 +28,50 @@ window.onload = function() {
   SimpleTest.waitForExplicitFinish();
 
   let gWalker = null;
-  let gClient = null;
+  let gInspectee = null;
 
   addTest(function setup() {
-    info ("Setting up inspector and walker actors.");
+    info("Setting up inspector and walker actors.");
 
     let url = document.getElementById("inspectorContent").href;
-    attachURL(url, function(err, client, tab, doc) {
+    attachURL(url, function (err, client, tab, doc) {
       gInspectee = doc;
       let inspector = InspectorFront(client, tab);
       promiseDone(inspector.getWalker().then(walker => {
         ok(walker, "getWalker() should return an actor.");
-        gClient = client;
         gWalker = walker;
       }).then(runNextTest));
     });
   });
 
   addAsyncTest(function* testXBLAnonymousInHTMLDocument() {
-    info ("Testing XBL anonymous in an HTML document.");
+    info("Testing XBL anonymous in an HTML document.");
     let rawToolbarbutton = gInspectee.createElementNS(XUL_NS, "toolbarbutton");
     gInspectee.documentElement.appendChild(rawToolbarbutton);
 
     let toolbarbutton = yield gWalker.querySelector(gWalker.rootNode, "toolbarbutton");
     let children = yield gWalker.children(toolbarbutton);
 
-    is (toolbarbutton.numChildren, 0, "XBL content is not visible in HTML doc");
-    is (children.nodes.length, 0, "XBL content is not returned in HTML doc");
+    is(toolbarbutton.numChildren, 0, "XBL content is not visible in HTML doc");
+    is(children.nodes.length, 0, "XBL content is not returned in HTML doc");
 
     runNextTest();
   });
 
   addAsyncTest(function* testNativeAnonymous() {
-    info ("Testing native anonymous content with walker.");
+    info("Testing native anonymous content with walker.");
 
     let select = yield gWalker.querySelector(gWalker.rootNode, "select");
     let children = yield gWalker.children(select);
 
-    is (select.numChildren, 2, "No native anon content for form control");
-    is (children.nodes.length, 2, "No native anon content for form control");
+    is(select.numChildren, 2, "No native anon content for form control");
+    is(children.nodes.length, 2, "No native anon content for form control");
 
     runNextTest();
   });
 
   addAsyncTest(function* testNativeAnonymousStartingNode() {
-    info ("Tests attaching an element that a walker can't see.");
+    info("Tests attaching an element that a walker can't see.");
 
     let serverWalker = DebuggerServer._searchAllConnectionsForActor(gWalker.actorID);
     let docwalker = new _documentWalker(
@@ -78,108 +79,109 @@ window.onload = function() {
       gInspectee.defaultView,
       nodeFilterConstants.SHOW_ALL,
       () => {
-        return nodeFilterConstants.FILTER_ACCEPT
+        return nodeFilterConstants.FILTER_ACCEPT;
       }
     );
     let scrollbar = docwalker.lastChild();
-    is (scrollbar.tagName, "scrollbar", "An anonymous child has been fetched");
+    is(scrollbar.tagName, "scrollbar", "An anonymous child has been fetched");
 
     let node = yield serverWalker.attachElement(scrollbar);
 
-    ok (node, "A response has arrived");
-    ok (node.node, "A node is in the response");
-    is (node.node.rawNode.tagName, "SELECT",
+    ok(node, "A response has arrived");
+    ok(node.node, "A node is in the response");
+    is(node.node.rawNode.tagName, "SELECT",
       "The node has changed to a parent that the walker recognizes");
 
     runNextTest();
   });
 
   addAsyncTest(function* testPseudoElements() {
-    info ("Testing pseudo elements with walker.");
+    info("Testing pseudo elements with walker.");
 
     // Markup looks like: <div><::before /><span /><::after /></div>
     let pseudo = yield gWalker.querySelector(gWalker.rootNode, "#pseudo");
     let children = yield gWalker.children(pseudo);
 
-    is (pseudo.numChildren, 1, "::before/::after are not counted if there is a child");
-    is (children.nodes.length, 3, "Correct number of children");
+    is(pseudo.numChildren, 1, "::before/::after are not counted if there is a child");
+    is(children.nodes.length, 3, "Correct number of children");
 
     let before = children.nodes[0];
-    ok (before.isAnonymous, "Child is anonymous");
-    ok (!before._form.isXBLAnonymous, "Child is not XBL anonymous");
-    ok (!before._form.isShadowAnonymous, "Child is not shadow anonymous");
-    ok (before._form.isNativeAnonymous, "Child is native anonymous");
+    ok(before.isAnonymous, "Child is anonymous");
+    ok(!before._form.isXBLAnonymous, "Child is not XBL anonymous");
+    ok(!before._form.isShadowAnonymous, "Child is not shadow anonymous");
+    ok(before._form.isNativeAnonymous, "Child is native anonymous");
 
     let span = children.nodes[1];
-    ok (!span.isAnonymous, "Child is not anonymous");
+    ok(!span.isAnonymous, "Child is not anonymous");
 
     let after = children.nodes[2];
-    ok (after.isAnonymous, "Child is anonymous");
-    ok (!after._form.isXBLAnonymous, "Child is not XBL anonymous");
-    ok (!after._form.isShadowAnonymous, "Child is not shadow anonymous");
-    ok (after._form.isNativeAnonymous, "Child is native anonymous");
+    ok(after.isAnonymous, "Child is anonymous");
+    ok(!after._form.isXBLAnonymous, "Child is not XBL anonymous");
+    ok(!after._form.isShadowAnonymous, "Child is not shadow anonymous");
+    ok(after._form.isNativeAnonymous, "Child is native anonymous");
 
     runNextTest();
   });
 
   addAsyncTest(function* testEmptyWithPseudo() {
-    info ("Testing elements with no childrent, except for pseudos.");
+    info("Testing elements with no childrent, except for pseudos.");
 
-    info ("Checking an element whose only child is a pseudo element");
+    info("Checking an element whose only child is a pseudo element");
     let pseudo = yield gWalker.querySelector(gWalker.rootNode, "#pseudo-empty");
     let children = yield gWalker.children(pseudo);
 
-    is (pseudo.numChildren, 1, "::before/::after are is counted if there are no other children");
-    is (children.nodes.length, 1, "Correct number of children");
+    is(pseudo.numChildren, 1,
+       "::before/::after are is counted if there are no other children");
+    is(children.nodes.length, 1, "Correct number of children");
 
     let before = children.nodes[0];
-    ok (before.isAnonymous, "Child is anonymous");
-    ok (!before._form.isXBLAnonymous, "Child is not XBL anonymous");
-    ok (!before._form.isShadowAnonymous, "Child is not shadow anonymous");
-    ok (before._form.isNativeAnonymous, "Child is native anonymous");
+    ok(before.isAnonymous, "Child is anonymous");
+    ok(!before._form.isXBLAnonymous, "Child is not XBL anonymous");
+    ok(!before._form.isShadowAnonymous, "Child is not shadow anonymous");
+    ok(before._form.isNativeAnonymous, "Child is native anonymous");
 
     runNextTest();
   });
 
   addAsyncTest(function* testShadowAnonymous() {
-    info ("Testing shadow DOM content.");
+    info("Testing shadow DOM content.");
 
     let shadow = yield gWalker.querySelector(gWalker.rootNode, "#shadow");
     let children = yield gWalker.children(shadow);
 
-    is (shadow.numChildren, 3, "Children of the shadow root are counted");
-    is (children.nodes.length, 3, "Children returned from walker");
+    is(shadow.numChildren, 3, "Children of the shadow root are counted");
+    is(children.nodes.length, 3, "Children returned from walker");
 
     let before = children.nodes[0];
-    ok (before.isAnonymous, "Child is anonymous");
-    ok (!before._form.isXBLAnonymous, "Child is not XBL anonymous");
-    ok (!before._form.isShadowAnonymous, "Child is not shadow anonymous");
-    ok (before._form.isNativeAnonymous, "Child is native anonymous");
+    ok(before.isAnonymous, "Child is anonymous");
+    ok(!before._form.isXBLAnonymous, "Child is not XBL anonymous");
+    ok(!before._form.isShadowAnonymous, "Child is not shadow anonymous");
+    ok(before._form.isNativeAnonymous, "Child is native anonymous");
 
     // <h3>Shadow <em>DOM</em></h3>
     let shadowChild1 = children.nodes[1];
-    ok (shadowChild1.isAnonymous, "Child is anonymous");
-    ok (!shadowChild1._form.isXBLAnonymous, "Child is not XBL anonymous");
-    ok (shadowChild1._form.isShadowAnonymous, "Child is shadow anonymous");
-    ok (!shadowChild1._form.isNativeAnonymous, "Child is not native anonymous");
+    ok(shadowChild1.isAnonymous, "Child is anonymous");
+    ok(!shadowChild1._form.isXBLAnonymous, "Child is not XBL anonymous");
+    ok(shadowChild1._form.isShadowAnonymous, "Child is shadow anonymous");
+    ok(!shadowChild1._form.isNativeAnonymous, "Child is not native anonymous");
 
     let shadowSubChildren = yield gWalker.children(children.nodes[1]);
-    is (shadowChild1.numChildren, 2, "Subchildren of the shadow root are counted");
-    is (shadowSubChildren.nodes.length, 2, "Subchildren are returned from walker");
+    is(shadowChild1.numChildren, 2, "Subchildren of the shadow root are counted");
+    is(shadowSubChildren.nodes.length, 2, "Subchildren are returned from walker");
 
     // <em>DOM</em>
     let shadowSubChild = children.nodes[1];
-    ok (shadowSubChild.isAnonymous, "Child is anonymous");
-    ok (!shadowSubChild._form.isXBLAnonymous, "Child is not XBL anonymous");
-    ok (shadowSubChild._form.isShadowAnonymous, "Child is shadow anonymous");
-    ok (!shadowSubChild._form.isNativeAnonymous, "Child is not native anonymous");
+    ok(shadowSubChild.isAnonymous, "Child is anonymous");
+    ok(!shadowSubChild._form.isXBLAnonymous, "Child is not XBL anonymous");
+    ok(shadowSubChild._form.isShadowAnonymous, "Child is shadow anonymous");
+    ok(!shadowSubChild._form.isNativeAnonymous, "Child is not native anonymous");
 
     // <select multiple></select>
     let shadowChild2 = children.nodes[2];
-    ok (shadowChild2.isAnonymous, "Child is anonymous");
-    ok (!shadowChild2._form.isXBLAnonymous, "Child is not XBL anonymous");
-    ok (shadowChild2._form.isShadowAnonymous, "Child is shadow anonymous");
-    ok (!shadowChild2._form.isNativeAnonymous, "Child is not native anonymous");
+    ok(shadowChild2.isAnonymous, "Child is anonymous");
+    ok(!shadowChild2._form.isXBLAnonymous, "Child is not XBL anonymous");
+    ok(shadowChild2._form.isShadowAnonymous, "Child is shadow anonymous");
+    ok(!shadowChild2._form.isNativeAnonymous, "Child is not native anonymous");
 
     runNextTest();
   });
diff --git a/devtools/server/tests/mochitest/test_inspector-changeattrs.html b/devtools/server/tests/mochitest/test_inspector-changeattrs.html
index 2c52f01cb7d9..b1415f77116b 100644
--- a/devtools/server/tests/mochitest/test_inspector-changeattrs.html
+++ b/devtools/server/tests/mochitest/test_inspector-changeattrs.html
@@ -11,31 +11,24 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gClient = null;
-var gWalker = null;
-var checkActorIDs = [];
-
-function assertOwnership() {
-  assertOwnershipTrees(gWalker);
-}
+let gInspectee = null;
+let gWalker = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -56,34 +49,36 @@ addTest(function testChangeAttrs() {
     // We're only going to test that the change hit the document.
     // There are other tests that make sure changes are propagated
     // to the client.
-    is(attrNode.getAttribute("data-newattr"), "newvalue", "Node should have the first new attribute");
-    is(attrNode.getAttribute("data-newattr2"), "newvalue", "Node should have the second new attribute.");
+    is(attrNode.getAttribute("data-newattr"), "newvalue",
+       "Node should have the first new attribute");
+    is(attrNode.getAttribute("data-newattr2"), "newvalue",
+       "Node should have the second new attribute.");
   }).then(() => {
     // Change an attribute.
     let list = attrFront.startModifyingAttributes();
     list.setAttribute("data-newattr", "changedvalue");
     return list.apply();
   }).then(() => {
-    is(attrNode.getAttribute("data-newattr"), "changedvalue", "Node should have the changed first value.");
-    is(attrNode.getAttribute("data-newattr2"), "newvalue", "Second value should remain unchanged.");
+    is(attrNode.getAttribute("data-newattr"), "changedvalue",
+       "Node should have the changed first value.");
+    is(attrNode.getAttribute("data-newattr2"), "newvalue",
+       "Second value should remain unchanged.");
   }).then(() => {
     let list = attrFront.startModifyingAttributes();
     list.removeAttribute("data-newattr2");
     return list.apply();
   }).then(() => {
-    is(attrNode.getAttribute("data-newattr"), "changedvalue", "Node should have the changed first value.");
+    is(attrNode.getAttribute("data-newattr"), "changedvalue",
+       "Node should have the changed first value.");
     ok(!attrNode.hasAttribute("data-newattr2"), "Second value should be removed.");
   }).then(runNextTest));
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gInspectee;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-changevalue.html b/devtools/server/tests/mochitest/test_inspector-changevalue.html
index 04d01e43d611..d7fc347b4016 100644
--- a/devtools/server/tests/mochitest/test_inspector-changevalue.html
+++ b/devtools/server/tests/mochitest/test_inspector-changevalue.html
@@ -11,31 +11,26 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const Ci = Components.interfaces;
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+const Ci = Components.interfaces;
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gClient = null;
-var gWalker = null;
-
-function assertOwnership() {
-  assertOwnershipTrees(gWalker);
-}
+let gInspectee = null;
+let gWalker = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -60,13 +55,10 @@ addTest(function testChangeValue() {
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gInspectee;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-dead-nodes.html b/devtools/server/tests/mochitest/test_inspector-dead-nodes.html
index 571ac5c1f665..a4f504793686 100644
--- a/devtools/server/tests/mochitest/test_inspector-dead-nodes.html
+++ b/devtools/server/tests/mochitest/test_inspector-dead-nodes.html
@@ -11,20 +11,21 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1121528
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker, gDoc;
+let gWalker = null;
+let gDoc = null;
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   let url = document.getElementById("inspectorContent").href;
 
   let def = promise.defer();
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     def.resolve({client, tab, doc});
   });
   let {client, tab, doc} = yield def.promise;
@@ -37,7 +38,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.parents(nodeFront) before the load completes shouldn't fail");
 
@@ -51,7 +52,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.children(nodeFront) before the load completes shouldn't fail");
 
@@ -65,7 +66,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.siblings(nodeFront) before the load completes shouldn't fail");
 
@@ -79,7 +80,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.nextSibling(nodeFront) before the load completes shouldn't fail");
 
@@ -93,7 +94,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.previousSibling(nodeFront) before the load completes shouldn't fail");
 
@@ -107,7 +108,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.addPseudoClassLock(nodeFront) before the load completes " +
     "shouldn't fail");
@@ -122,7 +123,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.removePseudoClassLock(nodeFront) before the load completes " +
     "shouldn't fail");
@@ -137,7 +138,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.clearPseudoClassLocks(nodeFront) before the load completes " +
     "shouldn't fail");
@@ -152,7 +153,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.innerHTML(nodeFront) before the load completes shouldn't fail");
 
@@ -166,7 +167,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.setInnerHTML(nodeFront) before the load completes shouldn't fail");
 
@@ -180,7 +181,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.outerHTML(nodeFront) before the load completes shouldn't fail");
 
@@ -194,7 +195,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.setOuterHTML(nodeFront) before the load completes shouldn't fail");
 
@@ -208,7 +209,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.insertAdjacentHTML(nodeFront) before the load completes shouldn't " +
     "fail");
@@ -224,7 +225,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.removeNode(nodeFront) before the load completes should throw");
 
@@ -243,7 +244,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.removeNodes([nodeFront]) before the load completes should throw");
 
@@ -264,7 +265,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.insertBefore(nodeFront, parent, null) before the load completes " +
     "shouldn't fail");
@@ -280,7 +281,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.insertBefore(nodeFront, parent, sibling) before the load completes " +
     "shouldn't fail");
@@ -297,7 +298,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.editTagName(nodeFront) before the load completes shouldn't fail");
 
@@ -311,7 +312,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.hideNode(nodeFront) before the load completes shouldn't fail");
 
@@ -325,7 +326,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.unhideNode(nodeFront) before the load completes shouldn't fail");
 
@@ -339,7 +340,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.releaseNode(nodeFront) before the load completes shouldn't fail");
 
@@ -353,7 +354,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   info("Getting a nodeFront, reloading the page, and calling " +
     "walker.querySelector(nodeFront) before the load completes shouldn't fail");
 
@@ -368,7 +369,8 @@ addAsyncTest(function*() {
 });
 
 addTest(function cleanup() {
-  gWalker = gDoc = null;
+  gWalker = null;
+  gDoc = null;
   runNextTest();
 });
   </script>
diff --git a/devtools/server/tests/mochitest/test_inspector-duplicate-node.html b/devtools/server/tests/mochitest/test_inspector-duplicate-node.html
index 68a4b93a1dcd..86f01e104ed4 100644
--- a/devtools/server/tests/mochitest/test_inspector-duplicate-node.html
+++ b/devtools/server/tests/mochitest/test_inspector-duplicate-node.html
@@ -11,30 +11,22 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1208864
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gClient = null;
-var gWalker = null;
-
-function assertOwnership() {
-  assertOwnershipTrees(gWalker);
-}
+let gWalker = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
-    gInspectee = doc;
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -55,9 +47,7 @@ addTest(Task.async(function* testDuplicateNode() {
 }));
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gInspectee;
-  delete gClient;
+  gWalker = null;
   runNextTest();
 });
   </script>
diff --git a/devtools/server/tests/mochitest/test_inspector-hide.html b/devtools/server/tests/mochitest/test_inspector-hide.html
index 9b7f1416a360..cf87b025ff86 100644
--- a/devtools/server/tests/mochitest/test_inspector-hide.html
+++ b/devtools/server/tests/mochitest/test_inspector-hide.html
@@ -11,25 +11,24 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gClient = null;
+let gWalker = null;
+let gInspectee = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -56,8 +55,8 @@ addTest(function testRearrange() {
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_inspector-insert.html b/devtools/server/tests/mochitest/test_inspector-insert.html
index 59500080b4c0..b9933ef4a0c2 100644
--- a/devtools/server/tests/mochitest/test_inspector-insert.html
+++ b/devtools/server/tests/mochitest/test_inspector-insert.html
@@ -11,29 +11,26 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
+"use strict";
+
 const inspector = require("devtools/server/actors/inspector");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gClient = null;
-
-function assertOwnership() {
-  return assertOwnershipTrees(gWalker);
-}
+let gWalker = null;
+let gInspectee = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
-    let inspector = InspectorFront(client, tab);
-    promiseDone(inspector.getWalker().then(walker => {
+    let inspectorFront = InspectorFront(client, tab);
+    promiseDone(inspectorFront.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -47,9 +44,11 @@ addAsyncTest(function* testRearrange() {
 
   // Move nodeA to the end of the list.
   yield gWalker.insertBefore(nodeA, longlist, null);
-  ok(!gInspectee.querySelector("#a").nextSibling, "a should now be at the end of the list.");
+  ok(!gInspectee.querySelector("#a").nextSibling,
+     "a should now be at the end of the list.");
   children = yield gWalker.children(longlist);
-  is(nodeA, children.nodes[children.nodes.length - 1], "a should now be the last returned child.");
+  is(nodeA, children.nodes[children.nodes.length - 1],
+     "a should now be the last returned child.");
 
   // Now move it to the middle of the list.
   let nextNode = children.nodes[13];
@@ -99,8 +98,8 @@ addAsyncTest(function* testInsertInvalidInput() {
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_inspector-mutations-attr.html b/devtools/server/tests/mochitest/test_inspector-mutations-attr.html
index 1117e2775437..5955669a6783 100644
--- a/devtools/server/tests/mochitest/test_inspector-mutations-attr.html
+++ b/devtools/server/tests/mochitest/test_inspector-mutations-attr.html
@@ -11,28 +11,26 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gWalker = null;
-var gClient = null;
-var attrNode;
-var attrFront;
+let gInspectee = null;
+let gWalker = null;
+let attrNode;
+let attrFront;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -50,14 +48,14 @@ addTest(testRemoveAttribute);
 addTest(testQueuedMutations);
 
 function setupAttrTest() {
-  attrNode = gInspectee.querySelector("#a")
+  attrNode = gInspectee.querySelector("#a");
   promiseDone(gWalker.querySelector(gWalker.rootNode, "#a").then(node => {
     attrFront = node;
   }).then(runNextTest));
 }
 
 function setupFrameAttrTest() {
-  let frame = gInspectee.querySelector('#childFrame');
+  let frame = gInspectee.querySelector("#childFrame");
   attrNode = frame.contentDocument.querySelector("#a");
 
   promiseDone(gWalker.querySelector(gWalker.rootNode, "#childFrame").then(childFrame => {
@@ -77,8 +75,10 @@ function testAddAttribute() {
   attrNode.setAttribute("data-newattr2", "newvalue");
   gWalker.once("mutations", () => {
     is(attrFront.attributes.length, 3, "Should have id and two new attributes.");
-    is(attrFront.getAttribute("data-newattr"), "newvalue", "Node front should have the first new attribute");
-    is(attrFront.getAttribute("data-newattr2"), "newvalue", "Node front should have the second new attribute.");
+    is(attrFront.getAttribute("data-newattr"), "newvalue",
+       "Node front should have the first new attribute");
+    is(attrFront.getAttribute("data-newattr2"), "newvalue",
+       "Node front should have the second new attribute.");
     runNextTest();
   });
 }
@@ -88,10 +88,13 @@ function testChangeAttribute() {
   attrNode.setAttribute("data-newattr", "changedvalue2");
   attrNode.setAttribute("data-newattr", "changedvalue3");
   gWalker.once("mutations", mutations => {
-    is(mutations.length, 1, "Only one mutation is sent for multiple queued attribute changes");
+    is(mutations.length, 1,
+       "Only one mutation is sent for multiple queued attribute changes");
     is(attrFront.attributes.length, 3, "Should have id and two new attributes.");
-    is(attrFront.getAttribute("data-newattr"), "changedvalue3", "Node front should have the changed first value");
-    is(attrFront.getAttribute("data-newattr2"), "newvalue", "Second value should remain unchanged.");
+    is(attrFront.getAttribute("data-newattr"), "changedvalue3",
+       "Node front should have the changed first value");
+    is(attrFront.getAttribute("data-newattr2"), "newvalue",
+       "Second value should remain unchanged.");
     runNextTest();
   });
 }
@@ -100,10 +103,11 @@ function testRemoveAttribute() {
   attrNode.removeAttribute("data-newattr2");
   gWalker.once("mutations", () => {
     is(attrFront.attributes.length, 2, "Should have id and one remaining attribute.");
-    is(attrFront.getAttribute("data-newattr"), "changedvalue3", "Node front should still have the first value");
+    is(attrFront.getAttribute("data-newattr"), "changedvalue3",
+       "Node front should still have the first value");
     ok(!attrFront.hasAttribute("data-newattr2"), "Second value should be removed.");
     runNextTest();
-  })
+  });
 }
 
 function testQueuedMutations() {
@@ -115,7 +119,7 @@ function testQueuedMutations() {
   attrNode.setAttribute("data-newattr", "2");
   attrNode.removeAttribute("data-newattr");
 
-  for (var i = 0; i <= 1000; i++) {
+  for (let i = 0; i <= 1000; i++) {
     attrNode.setAttribute("data-newattr2", i);
   }
 
@@ -132,26 +136,27 @@ function testQueuedMutations() {
   attrNode.removeAttribute("data-newattr4");
 
   gWalker.once("mutations", mutations => {
-    is(mutations.length, 4, "Only one mutation each is sent for multiple queued attribute changes");
-    is(attrFront.attributes.length, 3, "Should have id, data-newattr2, and data-newattr3.");
+    is(mutations.length, 4,
+       "Only one mutation each is sent for multiple queued attribute changes");
+    is(attrFront.attributes.length, 3,
+       "Should have id, data-newattr2, and data-newattr3.");
 
-    is(attrFront.getAttribute("data-newattr2"), "1000", "Node front should still have the correct value");
-    is(attrFront.getAttribute("data-newattr3"), "3", "Node front should still have the correct value");
+    is(attrFront.getAttribute("data-newattr2"), "1000",
+       "Node front should still have the correct value");
+    is(attrFront.getAttribute("data-newattr3"), "3",
+       "Node front should still have the correct value");
     ok(!attrFront.hasAttribute("data-newattr"), "Attribute value should be removed.");
     ok(!attrFront.hasAttribute("data-newattr4"), "Attribute value should be removed.");
 
     runNextTest();
-  })
+  });
 }
 
 addTest(function cleanup() {
-  delete gInspectee;
-  delete gWalker;
-  delete gClient;
+  gInspectee = null;
+  gWalker = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-mutations-childlist.html b/devtools/server/tests/mochitest/test_inspector-mutations-childlist.html
index 5e031af57443..687b2837f4c1 100644
--- a/devtools/server/tests/mochitest/test_inspector-mutations-childlist.html
+++ b/devtools/server/tests/mochitest/test_inspector-mutations-childlist.html
@@ -11,26 +11,24 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gWalker = null;
-var gClient = null;
-var gCleanupConnection = null;
+let gInspectee = null;
+let gWalker = null;
+let gCleanupConnection = null;
 
 function setup(callback) {
   let url = document.getElementById("inspectorContent").href;
-  gCleanupConnection = attachURL(url, function(err, client, tab, doc) {
+  gCleanupConnection = attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
-      gClient = client;
       gWalker = walker;
     }).then(callback));
   });
@@ -38,7 +36,6 @@ function setup(callback) {
 
 function teardown() {
   gWalker = null;
-  gClient = null;
   gInspectee = null;
   if (gCleanupConnection) {
     gCleanupConnection();
@@ -47,7 +44,7 @@ function teardown() {
 }
 
 function assertOwnership() {
-  let num = assertOwnershipTrees(gWalker);
+  return assertOwnershipTrees(gWalker);
 }
 
 function setParent(nodeSelector, newParentSelector) {
@@ -83,7 +80,7 @@ function doMoves(moves) {
 var gDummySerial = 0;
 
 function mutationTest(testSpec) {
-  return function() {
+  return function () {
     setup(() => {
       promiseDone(loadSelectors(testSpec.load || ["html"]).then(() => {
         gWalker.autoCleanup = !!testSpec.autoCleanup;
@@ -99,6 +96,7 @@ function mutationTest(testSpec) {
 
         gWalker.once("mutations", (mutations) => {
           // Filter out our dummy mutation.
+          // eslint-disable-next-line max-nested-callbacks
           mutations = mutations.filter(change => {
             if (change.type == "attributes" &&
                 change.attributeName == "data-dummy") {
@@ -114,14 +112,14 @@ function mutationTest(testSpec) {
           runNextTest();
         });
       }));
-    })
-  }
+    });
+  };
 }
 
 // Verify that our dummy mutation works.
 addTest(mutationTest({
   autoCleanup: false,
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 0, "Dummy mutation is filtered out.");
   }
 }));
@@ -134,17 +132,18 @@ addTest(mutationTest({
   moves: [
     ["#a", "#longlist"]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     let remove = mutations[0];
-    is(remove.type, "childList", "First mutation should be a childList.")
-    ok(remove.removed.length > 0, "First mutation should be a removal.")
+    is(remove.type, "childList", "First mutation should be a childList.");
+    ok(remove.removed.length > 0, "First mutation should be a removal.");
     let add = mutations[1];
-    is(add.type, "childList", "Second mutation should be a childList removal.")
-    ok(add.added.length > 0, "Second mutation should be an addition.")
+    is(add.type, "childList", "Second mutation should be a childList removal.");
+    ok(add.added.length > 0, "Second mutation should be an addition.");
     let a = add.added[0];
     is(a.id, "a", "Added node should be #a");
     is(a.parentNode(), remove.target, "Should still be a child of longlist.");
-    is(remove.target, add.target, "First and second mutations should be against the same node.");
+    is(remove.target, add.target,
+       "First and second mutations should be against the same node.");
   }
 }));
 
@@ -155,13 +154,13 @@ addTest(mutationTest({
   moves: [
     ["#a", "#longlist-sibling"]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     let remove = mutations[0];
-    is(remove.type, "childList", "First mutation should be a childList.")
-    ok(remove.removed.length > 0, "First mutation should be a removal.")
+    is(remove.type, "childList", "First mutation should be a childList.");
+    ok(remove.removed.length > 0, "First mutation should be a removal.");
     let add = mutations[1];
-    is(add.type, "childList", "Second mutation should be a childList removal.")
-    ok(add.added.length > 0, "Second mutation should be an addition.")
+    is(add.type, "childList", "Second mutation should be a childList removal.");
+    ok(add.added.length > 0, "Second mutation should be an addition.");
     let a = add.added[0];
     is(a.id, "a", "Added node should be #a");
     is(a.parentNode(), add.target, "Should still be a child of longlist.");
@@ -177,7 +176,7 @@ addTest(mutationTest({
   moves: [
     ["#longlist-sibling", "#longlist"]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 2, "Should generate two mutations");
     is(mutations[0].type, "childList", "Should be childList mutations.");
     is(mutations[0].added.length, 0, "Should have no adds.");
@@ -196,7 +195,7 @@ addTest(mutationTest({
   moves: [
     ["#longlist-sibling-firstchild", "#longlist"]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 1, "Should generate two mutations");
     is(mutations[0].type, "childList", "Should be childList mutations.");
     is(mutations[0].added.length, 0, "Should have no adds.");
@@ -211,7 +210,7 @@ addTest(mutationTest({
   moves: [
     ["#longlist-sibling", "#longlist"]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 0, "Should generate no mutations.");
   }
 }));
@@ -223,14 +222,15 @@ addTest(mutationTest({
   moves: [
     ["#longlist", null]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 1, "Should generate one mutation.");
     let change = mutations[0];
     is(change.type, "childList", "Should be a childList.");
     is(change.removed.length, 1, "Should have removed a child.");
     let ownership = clientOwnershipTree(gWalker);
     is(ownership.orphaned.length, 1, "Should have one orphaned subtree.");
-    is(ownershipTreeSize(ownership.orphaned[0]), 1 + 26 + 26, "Should have orphaned longlist, and 26 children, and 26 singleTextChilds");
+    is(ownershipTreeSize(ownership.orphaned[0]), 1 + 26 + 26,
+       "Should have orphaned longlist, and 26 children, and 26 singleTextChilds");
   }
 }));
 
@@ -241,7 +241,7 @@ addTest(mutationTest({
   moves: [
     ["#longlist", null]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 1, "Should generate one mutation.");
     let change = mutations[0];
     is(change.type, "childList", "Should be a childList.");
@@ -258,25 +258,27 @@ addTest(mutationTest({
   moves: [
     ["#longlist", "#longlist-sibling"]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 1, "Should generate one mutation.");
     let change = mutations[0];
     is(change.type, "childList", "Should be a childList.");
     is(change.removed.length, 1, "Should have removed a child.");
     let ownership = clientOwnershipTree(gWalker);
     is(ownership.orphaned.length, 1, "Should have one orphaned subtree.");
-    is(ownershipTreeSize(ownership.orphaned[0]), 1 + 26 + 26, "Should have orphaned longlist, 26 children, and 26 singleTextChilds.");
+    is(ownershipTreeSize(ownership.orphaned[0]), 1 + 26 + 26,
+       "Should have orphaned longlist, 26 children, and 26 singleTextChilds.");
   }
 }));
 
-// Orphan a node by moving it into the tree but out of our visible subtree, and clean it up.
+// Orphan a node by moving it into the tree but out of our visible subtree,
+// and clean it up.
 addTest(mutationTest({
   autoCleanup: true,
   load: ["#longlist div"],
   moves: [
     ["#longlist", "#longlist-sibling"]
   ],
-  postCheck: function(mutations) {
+  postCheck: function (mutations) {
     is(mutations.length, 1, "Should generate one mutation.");
     let change = mutations[0];
     is(change.type, "childList", "Should be a childList.");
@@ -286,15 +288,11 @@ addTest(mutationTest({
   }
 }));
 
-
 addTest(function cleanup() {
-  delete gInspectee;
-  delete gWalker;
-  delete gClient;
+  gInspectee = null;
+  gWalker = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-mutations-events.html b/devtools/server/tests/mochitest/test_inspector-mutations-events.html
index 6a4fde9b9517..c64313181459 100644
--- a/devtools/server/tests/mochitest/test_inspector-mutations-events.html
+++ b/devtools/server/tests/mochitest/test_inspector-mutations-events.html
@@ -10,9 +10,9 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1157469
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
+"use strict";
 
-window.onload = function() {
-
+window.onload = function () {
   const Cu = Components.utils;
   const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
   const {InspectorFront} = require("devtools/shared/fronts/inspector");
@@ -30,11 +30,11 @@ window.onload = function() {
   let eventFront2;
 
   addAsyncTest(function* setup() {
-    info ("Setting up inspector and walker actors.");
+    info("Setting up inspector and walker actors.");
     let url = document.getElementById("inspectorContent").href;
 
     yield new Promise(resolve => {
-      attachURL(url, function(err, client, tab, doc) {
+      attachURL(url, function (err, client, tab, doc) {
         inspectee = doc;
         inspector = InspectorFront(client, tab);
         resolve();
@@ -48,8 +48,8 @@ window.onload = function() {
   });
 
   addAsyncTest(function* setupEventTest() {
-    eventNode1 = inspectee.querySelector("#a")
-    eventNode2 = inspectee.querySelector("#b")
+    eventNode1 = inspectee.querySelector("#a");
+    eventNode2 = inspectee.querySelector("#b");
 
     eventFront1 = yield walker.querySelector(walker.rootNode, "#a");
     eventFront2 = yield walker.querySelector(walker.rootNode, "#b");
@@ -67,7 +67,8 @@ window.onload = function() {
     is(mutations.length, 1, "one mutation expected");
     is(mutations[0].target, eventFront1, "mutation targets eventFront1");
     is(mutations[0].type, "events", "mutation type is events");
-    is(mutations[0].hasEventListeners, true, "mutation target should have event listeners");
+    is(mutations[0].hasEventListeners, true,
+       "mutation target should have event listeners");
     is(eventFront1.hasEventListeners, true, "eventFront1 should have event listeners");
 
     info("remove event listener on a single node");
@@ -77,10 +78,12 @@ window.onload = function() {
     is(mutations.length, 1, "one mutation expected");
     is(mutations[0].target, eventFront1, "mutation targets eventFront1");
     is(mutations[0].type, "events", "mutation type is events");
-    is(mutations[0].hasEventListeners, false, "mutation target should have no event listeners");
-    is(eventFront1.hasEventListeners, false, "eventFront1 should have no event listeners");
+    is(mutations[0].hasEventListeners, false,
+       "mutation target should have no event listeners");
+    is(eventFront1.hasEventListeners, false,
+       "eventFront1 should have no event listeners");
 
-    info("perform several event listener changes on a single node")
+    info("perform several event listener changes on a single node");
     eventNode1.addEventListener("click", eventListener1);
     eventNode1.addEventListener("click", eventListener2);
     eventNode1.removeEventListener("click", eventListener1);
@@ -90,7 +93,8 @@ window.onload = function() {
     is(mutations.length, 1, "one mutation expected");
     is(mutations[0].target, eventFront1, "mutation targets eventFront1");
     is(mutations[0].type, "events", "mutation type is events");
-    is(mutations[0].hasEventListeners, false, "no event listener expected on mutation target");
+    is(mutations[0].hasEventListeners, false,
+       "no event listener expected on mutation target");
     is(eventFront1.hasEventListeners, false, "no event listener expected on node");
 
     runNextTest();
@@ -108,12 +112,14 @@ window.onload = function() {
     // first mutation
     is(mutations[0].target, eventFront1, "first mutation targets eventFront1");
     is(mutations[0].type, "events", "mutation type is events");
-    is(mutations[0].hasEventListeners, true, "mutation target should have event listeners");
+    is(mutations[0].hasEventListeners, true,
+       "mutation target should have event listeners");
     is(eventFront1.hasEventListeners, true, "eventFront1 should have event listeners");
     // second mutation
     is(mutations[1].target, eventFront2, "second mutation targets eventFront2");
     is(mutations[1].type, "events", "mutation type is events");
-    is(mutations[1].hasEventListeners, true, "mutation target should have event listeners");
+    is(mutations[1].hasEventListeners, true,
+       "mutation target should have event listeners");
     is(eventFront2.hasEventListeners, true, "eventFront1 should have event listeners");
 
     info("remove event listeners on both nodes");
@@ -125,13 +131,17 @@ window.onload = function() {
     // first mutation
     is(mutations[0].target, eventFront1, "first mutation targets eventFront1");
     is(mutations[0].type, "events", "mutation type is events");
-    is(mutations[0].hasEventListeners, false, "mutation target should have no event listeners");
-    is(eventFront1.hasEventListeners, false, "eventFront2 should have no event listeners");
+    is(mutations[0].hasEventListeners, false,
+       "mutation target should have no event listeners");
+    is(eventFront1.hasEventListeners, false,
+       "eventFront2 should have no event listeners");
     // second mutation
     is(mutations[1].target, eventFront2, "second mutation targets eventFront2");
     is(mutations[1].type, "events", "mutation type is events");
-    is(mutations[1].hasEventListeners, false, "mutation target should have no event listeners");
-    is(eventFront2.hasEventListeners, false, "eventFront2 should have no event listeners");
+    is(mutations[1].hasEventListeners, false,
+       "mutation target should have no event listeners");
+    is(eventFront2.hasEventListeners, false,
+       "eventFront2 should have no event listeners");
 
     runNextTest();
   });
@@ -142,7 +152,7 @@ window.onload = function() {
     info("try to remove an event listener not previously added");
     eventNode1.removeEventListener("click", eventListener1);
 
-    info("set any attribute on the node to trigger a mutation")
+    info("set any attribute on the node to trigger a mutation");
     eventNode1.setAttribute("data-attr", "somevalue");
 
     let mutations = yield waitForMutations();
@@ -153,9 +163,11 @@ window.onload = function() {
   });
 
   function checkNodesHaveNoEventListener() {
-    is(eventFront1.hasEventListeners, false, "eventFront1 hasEventListeners should be false");
-    is(eventFront2.hasEventListeners, false, "eventFront2 hasEventListeners should be false");
-  };
+    is(eventFront1.hasEventListeners, false,
+       "eventFront1 hasEventListeners should be false");
+    is(eventFront2.hasEventListeners, false,
+       "eventFront2 hasEventListeners should be false");
+  }
 
   function waitForMutations() {
     return new Promise(resolve => {
@@ -166,8 +178,7 @@ window.onload = function() {
   }
 
   runNextTest();
-}
-
+};
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-mutations-frameload.html b/devtools/server/tests/mochitest/test_inspector-mutations-frameload.html
index 0090f2363ca4..aebff8d878d2 100644
--- a/devtools/server/tests/mochitest/test_inspector-mutations-frameload.html
+++ b/devtools/server/tests/mochitest/test_inspector-mutations-frameload.html
@@ -11,23 +11,21 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gWalker = null;
-var gClient = null;
-var gChildFrame = null;
-var gChildDocument = null;
-var gCleanupConnection = null;
+let gInspectee = null;
+let gWalker = null;
+let gClient = null;
+let gCleanupConnection = null;
 
 function setup(callback) {
   let url = document.getElementById("inspectorContent").href;
-  gCleanupConnection = attachURL(url, function(err, client, tab, doc) {
+  gCleanupConnection = attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
@@ -42,7 +40,6 @@ function teardown() {
   gWalker = null;
   gClient = null;
   gInspectee = null;
-  gChildFrame = null;
   if (gCleanupConnection) {
     gCleanupConnection();
     gCleanupConnection = null;
@@ -55,8 +52,8 @@ function assertOwnership() {
 
 function loadChildSelector(selector) {
   return gWalker.querySelector(gWalker.rootNode, "#childFrame").then(frame => {
-    ok(frame.numChildren > 0, "Child frame should consider its loaded document as a child.");
-    gChildFrame = frame;
+    ok(frame.numChildren > 0,
+       "Child frame should consider its loaded document as a child.");
     return gWalker.children(frame);
   }).then(children => {
     return gWalker.querySelectorAll(children.nodes[0], selector);
@@ -76,7 +73,6 @@ function getUnloadedDoc(mutations) {
 
 addTest(function loadNewChild() {
   setup(() => {
-    let beforeUnloadSize = 0;
     // Load a bunch of fronts for actors inside the child frame.
     promiseDone(loadChildSelector("#longlist div").then(() => {
       let childFrame = gInspectee.querySelector("#childFrame");
@@ -102,7 +98,6 @@ addTest(function loadNewChild() {
 
 addTest(function loadNewChildTwice() {
   setup(() => {
-    let beforeUnloadSize = 0;
     // Load a bunch of fronts for actors inside the child frame.
     promiseDone(loadChildSelector("#longlist div").then(() => {
       let childFrame = gInspectee.querySelector("#childFrame");
@@ -130,10 +125,8 @@ addTest(function loadNewChildTwice() {
   });
 });
 
-
 addTest(function loadNewChildTwiceAndCareAboutIt() {
   setup(() => {
-    let beforeUnloadSize = 0;
     // Load a bunch of fronts for actors inside the child frame.
     promiseDone(loadChildSelector("#longlist div").then(() => {
       let childFrame = gInspectee.querySelector("#childFrame");
@@ -168,7 +161,6 @@ addTest(function loadNewChildTwiceAndCareAboutIt() {
 
 addTest(function testBack() {
   setup(() => {
-    let beforeUnloadSize = 0;
     // Load a bunch of fronts for actors inside the child frame.
     promiseDone(loadChildSelector("#longlist div").then(() => {
       let childFrame = gInspectee.querySelector("#childFrame");
@@ -178,7 +170,8 @@ addTest(function testBack() {
       // Read the new child
       return loadChildSelector("#longlist div");
     }).then(() => {
-      // Now use history.back to change the source, and expect the same results as loadNewChild.
+      // Now use history.back to change the source,
+      // and expect the same results as loadNewChild.
       let childFrame = gInspectee.querySelector("#childFrame");
       childFrame.contentWindow.history.back();
       return waitForMutation(gWalker, isChildList);
diff --git a/devtools/server/tests/mochitest/test_inspector-mutations-value.html b/devtools/server/tests/mochitest/test_inspector-mutations-value.html
index 52072bd6e2fc..fab3fd0473a6 100644
--- a/devtools/server/tests/mochitest/test_inspector-mutations-value.html
+++ b/devtools/server/tests/mochitest/test_inspector-mutations-value.html
@@ -11,39 +11,38 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
+"use strict";
+
 const inspector = require("devtools/server/actors/inspector");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
 const testSummaryLength = 10;
 inspector.setValueSummaryLength(testSummaryLength);
-SimpleTest.registerCleanupFunction(function() {
+SimpleTest.registerCleanupFunction(function () {
   inspector.setValueSummaryLength(inspector.DEFAULT_VALUE_SUMMARY_LENGTH);
 });
 
-var gInspectee = null;
-var gWalker = null;
-var gClient = null;
-var valueNode;
+let gInspectee = null;
+let gWalker = null;
+let valueNode;
 var valueFront;
 var longStringFront;
 var longString = "stringstringstringstringstringstringstringstringstringstringstring";
-var truncatedLongString = longString.substring(0, testSummaryLength);
 var shortString = "str";
 var shortString2 = "str2";
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
-    let inspector = InspectorFront(client, tab);
-    promiseDone(inspector.getWalker().then(walker => {
+    let inspectorFront = InspectorFront(client, tab);
+    promiseDone(inspectorFront.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -71,7 +70,7 @@ function setupValueTest() {
 }
 
 function setupFrameValueTest() {
-  let frame = gInspectee.querySelector('#childFrame');
+  let frame = gInspectee.querySelector("#childFrame");
   valueNode = frame.contentDocument.querySelector("#longstring").firstChild;
 
   promiseDone(gWalker.querySelector(gWalker.rootNode, "#childFrame").then(childFrame => {
@@ -94,7 +93,7 @@ function checkNodeFrontValue(front, expectedValue) {
     return longstring.string();
   }).then(str => {
     is(str, expectedValue, "Node value is as expected");
-  })
+  });
 }
 
 function testKeepLongValue() {
@@ -147,9 +146,8 @@ function testSetLongValue() {
 }
 
 addTest(function cleanup() {
-  delete gInspectee;
-  delete gWalker;
-  delete gClient;
+  gInspectee = null;
+  gWalker = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_inspector-pick-color.html b/devtools/server/tests/mochitest/test_inspector-pick-color.html
index 8ac7bcb89abb..7b70252dff84 100644
--- a/devtools/server/tests/mochitest/test_inspector-pick-color.html
+++ b/devtools/server/tests/mochitest/test_inspector-pick-color.html
@@ -1,101 +1,99 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-Test that the inspector actor has the pickColorFromPage and cancelPickColorFromPage
-methods and that when a color is picked the color-picked event is emitted and that when
-the eyedropper is dimissed, the color-pick-canceled event is emitted.
-https://bugzilla.mozilla.org/show_bug.cgi?id=1262439
--->
-<head>
-  <meta charset="utf-8">
-  <title>Test for Bug 1262439</title>
-  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
-  <script type="application/javascript" src="inspector-helpers.js"></script>
-  <script type="application/javascript">
-window.onload = function() {
-  const Cu = Components.utils;
-  Cu.import("resource://devtools/shared/Loader.jsm");
-  const {Promise: promise} = Cu.import("resource://gre/modules/Promise.jsm", {});
-  const {InspectorFront} = devtools.require("devtools/shared/fronts/inspector");
-  const {console} = Cu.import("resource://gre/modules/Console.jsm", {});
-
-  SimpleTest.waitForExplicitFinish();
-
-  let win = null;
-  let inspector = null;
-
-  addAsyncTest(function*() {
-    info("Setting up inspector actor");
-
-    let url = document.getElementById("inspectorContent").href;
-
-    yield new Promise(resolve => {
-      attachURL(url, function(err, client, tab, doc) {
-        win = doc.defaultView;
-        inspector = InspectorFront(client, tab);
-        resolve();
-      });
-    });
-
-    runNextTest();
-  });
-
-  addAsyncTest(function*() {
-    info("Start picking a color from the page");
-    yield inspector.pickColorFromPage();
-
-    info("Click in the page and make sure a color-picked event is received");
-    let onColorPicked = waitForEvent("color-picked");
-    win.document.body.click();
-    let color = yield onColorPicked;
-
-    is(color, "#000000", "The color-picked event was received with the right color");
-
-    runNextTest();
-  });
-
-  addAsyncTest(function*() {
-    info("Start picking a color from the page");
-    yield inspector.pickColorFromPage();
-
-    info("Use the escape key to dismiss the eyedropper");
-    let onPickCanceled = waitForEvent("color-pick-canceled");
-
-    let keyboardEvent = win.document.createEvent("KeyboardEvent");
-    keyboardEvent.initKeyEvent("keydown", true, true, win, false, false,
-                               false, false, 27, 0);
-    win.document.dispatchEvent(keyboardEvent);
-
-    yield onPickCanceled;
-    ok(true, "The color-pick-canceled event was received");
-
-    runNextTest();
-  });
-
-  addAsyncTest(function*() {
-    info("Start picking a color from the page");
-    yield inspector.pickColorFromPage();
-
-    info("And cancel the color picking");
-    yield inspector.cancelPickColorFromPage();
-
-    runNextTest();
-  });
-
-  function waitForEvent(name) {
-    return new Promise(resolve => inspector.once(name, resolve));
-  }
-
-  runNextTest();
-};
-  </script>
-</head>
-<body>
-<a id="inspectorContent" target="_blank" href="inspector-eyedropper.html">Test Document</a>
-<p id="display"></p>
-<div id="content" style="display: none"></div>
-<pre id="test">
-</pre>
-</body>
-</html>
+<!DOCTYPE HTML>
+<html>
+<!--
+Test that the inspector actor has the pickColorFromPage and cancelPickColorFromPage
+methods and that when a color is picked the color-picked event is emitted and that when
+the eyedropper is dimissed, the color-pick-canceled event is emitted.
+https://bugzilla.mozilla.org/show_bug.cgi?id=1262439
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1262439</title>
+  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
+  <script type="application/javascript" src="inspector-helpers.js"></script>
+  <script type="application/javascript">
+"use strict";
+
+window.onload = function () {
+  const {InspectorFront} = require("devtools/shared/fronts/inspector");
+
+  SimpleTest.waitForExplicitFinish();
+
+  let win = null;
+  let inspector = null;
+
+  addAsyncTest(function* () {
+    info("Setting up inspector actor");
+
+    let url = document.getElementById("inspectorContent").href;
+
+    yield new Promise(resolve => {
+      attachURL(url, function (err, client, tab, doc) {
+        win = doc.defaultView;
+        inspector = InspectorFront(client, tab);
+        resolve();
+      });
+    });
+
+    runNextTest();
+  });
+
+  addAsyncTest(function* () {
+    info("Start picking a color from the page");
+    yield inspector.pickColorFromPage();
+
+    info("Click in the page and make sure a color-picked event is received");
+    let onColorPicked = waitForEvent("color-picked");
+    win.document.body.click();
+    let color = yield onColorPicked;
+
+    is(color, "#000000", "The color-picked event was received with the right color");
+
+    runNextTest();
+  });
+
+  addAsyncTest(function* () {
+    info("Start picking a color from the page");
+    yield inspector.pickColorFromPage();
+
+    info("Use the escape key to dismiss the eyedropper");
+    let onPickCanceled = waitForEvent("color-pick-canceled");
+
+    let keyboardEvent = win.document.createEvent("KeyboardEvent");
+    keyboardEvent.initKeyEvent("keydown", true, true, win, false, false,
+                               false, false, 27, 0);
+    win.document.dispatchEvent(keyboardEvent);
+
+    yield onPickCanceled;
+    ok(true, "The color-pick-canceled event was received");
+
+    runNextTest();
+  });
+
+  addAsyncTest(function* () {
+    info("Start picking a color from the page");
+    yield inspector.pickColorFromPage();
+
+    info("And cancel the color picking");
+    yield inspector.cancelPickColorFromPage();
+
+    runNextTest();
+  });
+
+  function waitForEvent(name) {
+    return new Promise(resolve => inspector.once(name, resolve));
+  }
+
+  runNextTest();
+};
+  </script>
+</head>
+<body>
+<a id="inspectorContent" target="_blank" href="inspector-eyedropper.html">Test Document</a>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/devtools/server/tests/mochitest/test_inspector-pseudoclass-lock.html b/devtools/server/tests/mochitest/test_inspector-pseudoclass-lock.html
index cc3810835404..3b8a798551d2 100644
--- a/devtools/server/tests/mochitest/test_inspector-pseudoclass-lock.html
+++ b/devtools/server/tests/mochitest/test_inspector-pseudoclass-lock.html
@@ -11,30 +11,29 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
-const DOMUtils = Components.classes["@mozilla.org/inspector/dom-utils;1"].
-                   getService(Components.interfaces.inIDOMUtils);
+"use strict";
 
-const KNOWN_PSEUDOCLASSES = [':hover', ':active', ':focus']
+const DOMUtils = Components.classes["@mozilla.org/inspector/dom-utils;1"]
+                           .getService(Components.interfaces.inIDOMUtils);
 
-window.onload = function() {
+const KNOWN_PSEUDOCLASSES = [":hover", ":active", ":focus"];
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gWalker = null;
-var gClient = null;
-var gCleanupConnection = null;
+let gInspectee = null;
+let gWalker = null;
+let gCleanupConnection = null;
 
 function setup(callback) {
   let url = document.getElementById("inspectorContent").href;
-  gCleanupConnection = attachURL(url, function(err, client, tab, doc) {
+  gCleanupConnection = attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
-      gClient = client;
       gWalker = walker;
     }).then(callback));
   });
@@ -42,7 +41,6 @@ function setup(callback) {
 
 function teardown() {
   gWalker = null;
-  gClient = null;
   gInspectee = null;
   if (gCleanupConnection) {
     gCleanupConnection();
@@ -53,10 +51,13 @@ function teardown() {
 function checkChange(change, expectation) {
   is(change.type, "pseudoClassLock", "Expect a pseudoclass lock change.");
   let target = change.target;
-  if (expectation.id)
+  if (expectation.id) {
     is(target.id, expectation.id, "Expect a change on node id " + expectation.id);
-  if (expectation.nodeName)
-    is(target.nodeName, expectation.nodeName, "Expect a change on node name " + expectation.nodeName);
+  }
+  if (expectation.nodeName) {
+    is(target.nodeName, expectation.nodeName,
+       "Expect a change on node name " + expectation.nodeName);
+  }
 
   is(target.pseudoClassLocks.length, expectation.pseudos.length,
      "Expect " + expectation.pseudos.length + " pseudoclass locks.");
@@ -74,7 +75,8 @@ function checkChange(change, expectation) {
   for (let pseudo of KNOWN_PSEUDOCLASSES) {
     if (!expectation.pseudos.some(expected => pseudo === expected)) {
       ok(!target.hasPseudoClassLock(pseudo), "Don't expect lock: " + pseudo);
-      ok(!DOMUtils.hasPseudoClassLock(target.rawNode(), pseudo), "Don't expect lock in dom: " + pseudo);
+      ok(!DOMUtils.hasPseudoClassLock(target.rawNode(), pseudo),
+         "Don't expect lock in dom: " + pseudo);
     }
   }
 }
@@ -82,7 +84,7 @@ function checkChange(change, expectation) {
 function checkMutations(mutations, expectations) {
   is(mutations.length, expectations.length, "Should get the right number of mutations.");
   for (let i = 0; i < mutations.length; i++) {
-    checkChange(mutations[i] , expectations[i]);
+    checkChange(mutations[i], expectations[i]);
   }
 }
 
@@ -94,7 +96,7 @@ addTest(function testPseudoClassLock() {
     return promiseDone(gWalker.querySelector(gWalker.rootNode, "#b").then(front => {
       nodeFront = front;
       // Lock the pseudoclass alone, no parents.
-      gWalker.addPseudoClassLock(nodeFront, ':active');
+      gWalker.addPseudoClassLock(nodeFront, ":active");
       // Expect a single pseudoClassLock mutation.
       return promiseOnce(gWalker, "mutations");
     }).then(mutations => {
@@ -107,50 +109,50 @@ addTest(function testPseudoClassLock() {
       });
     }).then(() => {
       // Now add :hover, this time with parents.
-      gWalker.addPseudoClassLock(nodeFront, ':hover', {parents: true});
+      gWalker.addPseudoClassLock(nodeFront, ":hover", {parents: true});
       return promiseOnce(gWalker, "mutations");
     }).then(mutations => {
       let expectedMutations = [{
-        id: 'b',
-        nodeName: 'DIV',
-        pseudos: [':hover', ':active'],
+        id: "b",
+        nodeName: "DIV",
+        pseudos: [":hover", ":active"],
       },
       {
-        id: 'longlist',
-        nodeName: 'DIV',
-        pseudos: [':hover']
+        id: "longlist",
+        nodeName: "DIV",
+        pseudos: [":hover"]
       },
       {
-        nodeName: 'BODY',
-        pseudos: [':hover']
+        nodeName: "BODY",
+        pseudos: [":hover"]
       },
       {
-        nodeName: 'HTML',
-        pseudos: [':hover']
+        nodeName: "HTML",
+        pseudos: [":hover"]
       }];
       checkMutations(mutations, expectedMutations);
     }).then(() => {
       // Now remove the :hover on all parents
-      gWalker.removePseudoClassLock(nodeFront, ':hover', {parents: true});
+      gWalker.removePseudoClassLock(nodeFront, ":hover", {parents: true});
       return promiseOnce(gWalker, "mutations");
     }).then(mutations => {
       let expectedMutations = [{
-        id: 'b',
-        nodeName: 'DIV',
+        id: "b",
+        nodeName: "DIV",
         // Should still have :active on the original node.
-        pseudos: [':active']
+        pseudos: [":active"]
       },
       {
-        id: 'longlist',
-        nodeName: 'DIV',
+        id: "longlist",
+        nodeName: "DIV",
         pseudos: []
       },
       {
-        nodeName: 'BODY',
+        nodeName: "BODY",
         pseudos: []
       },
       {
-        nodeName: 'HTML',
+        nodeName: "HTML",
         pseudos: []
       }];
       checkMutations(mutations, expectedMutations);
@@ -170,7 +172,8 @@ addTest(function testPseudoClassLock() {
       // Now shut down the walker and make sure that clears up the remaining lock.
       return gWalker.release();
     }).then(() => {
-      ok(!DOMUtils.hasPseudoClassLock(contentNode, ':active'), "Pseudoclass should have been removed during destruction.");
+      ok(!DOMUtils.hasPseudoClassLock(contentNode, ":active"),
+         "Pseudoclass should have been removed during destruction.");
       teardown();
     }).then(runNextTest));
   });
diff --git a/devtools/server/tests/mochitest/test_inspector-release.html b/devtools/server/tests/mochitest/test_inspector-release.html
index ae57538eddc8..94fb0652f26a 100644
--- a/devtools/server/tests/mochitest/test_inspector-release.html
+++ b/devtools/server/tests/mochitest/test_inspector-release.html
@@ -11,15 +11,15 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gClient = null;
+let gWalker = null;
+let gClient = null;
 
 function assertOwnership() {
   return assertOwnershipTrees(gWalker);
@@ -27,7 +27,7 @@ function assertOwnership() {
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
@@ -45,7 +45,8 @@ addTest(function testReleaseSubtree() {
   promiseDone(gWalker.querySelectorAll(gWalker.rootNode, "#longlist div").then(list => {
     // Make sure we have the 26 children of longlist in our ownership tree.
     is(list.length, 26, "Expect 26 div children.");
-    // Make sure we've read in all those children and incorporated them in our ownership tree.
+    // Make sure we've read in all those children and incorporated them
+    // in our ownership tree.
     return list.items();
   }).then((items)=> {
     originalOwnershipSize = assertOwnership();
@@ -69,7 +70,8 @@ addTest(function testReleaseSubtree() {
     longlist = node.actorID;
     return gWalker.releaseNode(node);
   }).then(() => {
-    // Our ownership size should now be 53 fewer (we forgot about #longlist + 26 children + 26 singleTextChild nodes)
+    // Our ownership size should now be 53 fewer
+    // (we forgot about #longlist + 26 children + 26 singleTextChild nodes)
     let newOwnershipSize = assertOwnership();
     is(newOwnershipSize, originalOwnershipSize - 53,
       "Ownership tree should be lower");
@@ -81,12 +83,10 @@ addTest(function testReleaseSubtree() {
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gClient;
+  gWalker = null;
+  gClient = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-reload.html b/devtools/server/tests/mochitest/test_inspector-reload.html
index 44a54be8288f..55bad8061f6b 100644
--- a/devtools/server/tests/mochitest/test_inspector-reload.html
+++ b/devtools/server/tests/mochitest/test_inspector-reload.html
@@ -11,26 +11,24 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gClient = null;
-var gWalker = null;
+let gInspectee = null;
+let gWalker = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
       return inspector.getWalker();
     }).then(walker => {
@@ -41,7 +39,6 @@ addTest(function setup() {
 });
 
 addTest(function testReload() {
-  let nodeFront;
   let oldRootID = gWalker.rootNode.actorID;
   // Load a node to populate the tree a bit.
   promiseDone(gWalker.querySelector(gWalker.rootNode, "#a").then(front => {
@@ -58,13 +55,10 @@ addTest(function testReload() {
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gInspectee;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-remove.html b/devtools/server/tests/mochitest/test_inspector-remove.html
index ef08121d2d08..88addf9e2052 100644
--- a/devtools/server/tests/mochitest/test_inspector-remove.html
+++ b/devtools/server/tests/mochitest/test_inspector-remove.html
@@ -11,15 +11,16 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gClient = null;
+let gWalker = null;
+let gClient = null;
+let gInspectee = null;
 
 function assertOwnership() {
   return assertOwnershipTrees(gWalker);
@@ -33,7 +34,7 @@ function ignoreNode(node) {
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
@@ -80,8 +81,10 @@ addTest(function testRemoveSubtree() {
     is(originalOwnershipSize, 56, "Correct number of items in ownership tree");
     return gWalker.removeNode(longlist);
   }).then(siblings => {
-    is(siblings.previousSibling.rawNode(), previousSibling, "Should have returned the previous sibling.");
-    is(siblings.nextSibling.rawNode(), nextSibling, "Should have returned the next sibling.");
+    is(siblings.previousSibling.rawNode(), previousSibling,
+       "Should have returned the previous sibling.");
+    is(siblings.nextSibling.rawNode(), nextSibling,
+       "Should have returned the next sibling.");
     return waitForMutation(gWalker, isChildList);
   }).then(() => {
     // Our ownership size should now be 51 fewer (we forgot about #longlist + 26
@@ -96,12 +99,11 @@ addTest(function testRemoveSubtree() {
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gClient;
+  gWalker = null;
+  gClient = null;
+  gInspectee = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector-resize.html b/devtools/server/tests/mochitest/test_inspector-resize.html
index 7d0b91850e4f..27f3502ed2fc 100644
--- a/devtools/server/tests/mochitest/test_inspector-resize.html
+++ b/devtools/server/tests/mochitest/test_inspector-resize.html
@@ -11,12 +11,13 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1222409
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   const Cu = Components.utils;
   const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
   const promise = require("promise");
   const {InspectorFront} = require("devtools/shared/fronts/inspector");
-  const {console} = Cu.import("resource://gre/modules/Console.jsm", {});
 
   SimpleTest.waitForExplicitFinish();
 
@@ -24,12 +25,13 @@ window.onload = function() {
   let inspector = null;
 
   addAsyncTest(function* setup() {
-    info ("Setting up inspector and walker actors.");
+    info("Setting up inspector and walker actors.");
 
     let url = document.getElementById("inspectorContent").href;
 
+    // eslint-disable-next-line new-cap
     yield new promise(resolve => {
-      attachURL(url, function(err, client, tab, doc) {
+      attachURL(url, function (err, client, tab, doc) {
         win = doc.defaultView;
         inspector = InspectorFront(client, tab);
         resolve();
@@ -39,7 +41,7 @@ window.onload = function() {
     runNextTest();
   });
 
-  addAsyncTest(function*() {
+  addAsyncTest(function* () {
     let walker = yield inspector.getWalker();
 
     // We can't receive events from the walker if we haven't first executed a
@@ -47,6 +49,7 @@ window.onload = function() {
     yield walker.querySelector(walker.rootNode, "img");
 
     let {outerWidth, outerHeight} = win;
+    // eslint-disable-next-line new-cap
     let onResize = new promise(resolve => {
       walker.once("resize", () => {
         resolve();
diff --git a/devtools/server/tests/mochitest/test_inspector-resolve-url.html b/devtools/server/tests/mochitest/test_inspector-resolve-url.html
index 7e59313cbe95..dbced06130ef 100644
--- a/devtools/server/tests/mochitest/test_inspector-resolve-url.html
+++ b/devtools/server/tests/mochitest/test_inspector-resolve-url.html
@@ -11,19 +11,19 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=921102
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspector;
-var gDoc;
+let gInspector;
+let gDoc;
 
-addTest(function() {
+addTest(function () {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gDoc = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     gInspector = InspectorFront(client, tab);
@@ -31,7 +31,7 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   info("Resolve a relative URL without providing a context node");
   gInspector.resolveRelativeURL("test.png?id=4#wow").then(url => {
     is(url, "chrome://mochitests/content/chrome/devtools/server/tests/" +
@@ -40,16 +40,16 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   info("Resolve an absolute URL without providing a context node");
   gInspector.resolveRelativeURL("chrome://mochitests/content/chrome/" +
-                                "devtools/server/").then(url => {
-    is(url, "chrome://mochitests/content/chrome/devtools/server/");
-    runNextTest();
-  });
+    "devtools/server/").then(url => {
+      is(url, "chrome://mochitests/content/chrome/devtools/server/");
+      runNextTest();
+    });
 });
 
-addTest(function() {
+addTest(function () {
   info("Resolve a relative URL providing a context node");
   let node = gDoc.querySelector(".big-horizontal");
   gInspector.resolveRelativeURL("test.png?id=4#wow", node).then(url => {
@@ -59,18 +59,19 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   info("Resolve an absolute URL providing a context node");
   let node = gDoc.querySelector(".big-horizontal");
   gInspector.resolveRelativeURL("chrome://mochitests/content/chrome/" +
-                                "devtools/server/", node).then(url => {
-    is(url, "chrome://mochitests/content/chrome/devtools/server/");
-    runNextTest();
-  });
+    "devtools/server/", node).then(url => {
+      is(url, "chrome://mochitests/content/chrome/devtools/server/");
+      runNextTest();
+    });
 });
 
-addTest(function() {
-  gInspector = gDoc = null;
+addTest(function () {
+  gInspector = null;
+  gDoc = null;
   runNextTest();
 });
   </script>
diff --git a/devtools/server/tests/mochitest/test_inspector-retain.html b/devtools/server/tests/mochitest/test_inspector-retain.html
index ceff4a8560fb..ee0f0f2a7c1d 100644
--- a/devtools/server/tests/mochitest/test_inspector-retain.html
+++ b/devtools/server/tests/mochitest/test_inspector-retain.html
@@ -11,16 +11,15 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gClient = null;
-var gInspectee = null;
+let gWalker = null;
+let gInspectee = null;
 
 function assertOwnership() {
   return assertOwnershipTrees(gWalker);
@@ -28,13 +27,12 @@ function assertOwnership() {
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -50,7 +48,6 @@ addTest(function setup() {
 addTest(function testRetain() {
   let originalOwnershipSize = 0;
   let bodyFront = null;
-  let frameFront = null;
   let childListFront = null;
   // Get the toplevel body element and retain it.
   promiseDone(gWalker.querySelector(gWalker.rootNode, "body").then(front => {
@@ -60,7 +57,6 @@ addTest(function testRetain() {
     // Get an element in the child frame and retain it.
     return gWalker.querySelector(gWalker.rootNode, "#childFrame");
   }).then(frame => {
-    frameFront = frame;
     return gWalker.children(frame, { maxNodes: 1 }).then(children => {
       return children.nodes[0];
     });
@@ -75,7 +71,6 @@ addTest(function testRetain() {
     // OK, try releasing the parent of the first retained.
     return gWalker.releaseNode(bodyFront.parentNode());
   }).then(() => {
-    let size = assertOwnership();
     let clientTree = clientOwnershipTree(gWalker);
 
     // That request should have freed the parent of the first retained
@@ -84,26 +79,25 @@ addTest(function testRetain() {
        originalOwnershipSize,
        "Should have only lost one item overall.");
     is(gWalker._retainedOrphans.size, 1, "Should have retained one orphan");
-    ok(gWalker._retainedOrphans.has(bodyFront), "Should have retained the expected node.");
+    ok(gWalker._retainedOrphans.has(bodyFront),
+       "Should have retained the expected node.");
   }).then(() => {
     // Unretain the body, which should promote the childListFront to a retained orphan.
     return gWalker.unretainNode(bodyFront);
   }).then(() => {
     assertOwnership();
-    let clientTree = clientOwnershipTree(gWalker);
 
     is(gWalker._retainedOrphans.size, 1, "Should still only have one retained orphan.");
-    ok(!gWalker._retainedOrphans.has(bodyFront), "Should have dropped the body node.")
-    ok(gWalker._retainedOrphans.has(childListFront), "Should have retained the child node.")
+    ok(!gWalker._retainedOrphans.has(bodyFront), "Should have dropped the body node.");
+    ok(gWalker._retainedOrphans.has(childListFront),
+       "Should have retained the child node.");
   }).then(() => {
     // Change the source of the iframe, which should kill the retained orphan.
     gInspectee.querySelector("#childFrame").src = "data:text/html,<html>new child</html>";
     return waitForMutation(gWalker, isUnretained);
   }).then(mutations => {
     assertOwnership();
-    let clientTree = clientOwnershipTree(gWalker);
     is(gWalker._retainedOrphans.size, 0, "Should have no more retained orphans.");
-
   }).then(runNextTest));
 });
 
@@ -123,14 +117,12 @@ addTest(function testWinRace() {
     ]);
   }).then(() => {
     assertOwnership();
-    let clientTree = clientOwnershipTree(gWalker);
     is(gWalker._retainedOrphans.size, 1, "Should have a retained orphan.");
     ok(gWalker._retainedOrphans.has(front), "Should have retained our expected node.");
     return gWalker.unretainNode(front);
   }).then(() => {
     // Make sure we're clear for the next test.
     assertOwnership();
-    let clientTree = clientOwnershipTree(gWalker);
     is(gWalker._retainedOrphans.size, 0, "Should have no more retained orphans.");
   }).then(runNextTest));
 });
@@ -149,19 +141,18 @@ addTest(function testLoseRace() {
     // Verify that we have an outstanding request (no good way to tell that it's a
     // getMutations request, but there's nothing else it would be).
     is(gWalker._requests.length, 1, "Should have an outstanding request.");
-    return gWalker.retainNode(front)
-  }).then(() => { ok(false, "Request should not have succeeded!"); },
+    return gWalker.retainNode(front);
+  }).then(() => ok(false, "Request should not have succeeded!"),
           (err) => {
-    ok(err, "noSuchActor", "Should have lost the race.");
-    let clientTree = clientOwnershipTree(gWalker);
-    is(gWalker._retainedOrphans.size, 0, "Should have no more retained orphans.");
-    // Don't re-throw the error.
-  }).then(runNextTest));
+            ok(err, "noSuchActor", "Should have lost the race.");
+            is(gWalker._retainedOrphans.size, 0, "Should have no more retained orphans.");
+            // Don't re-throw the error.
+          }).then(runNextTest));
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_inspector-scroll-into-view.html b/devtools/server/tests/mochitest/test_inspector-scroll-into-view.html
index 5fc1c4eeacaa..b783d5153484 100644
--- a/devtools/server/tests/mochitest/test_inspector-scroll-into-view.html
+++ b/devtools/server/tests/mochitest/test_inspector-scroll-into-view.html
@@ -11,30 +11,24 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=901250
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gClient = null;
-var gWalker = null;
-
-function assertOwnership() {
-  assertOwnershipTrees(gWalker);
-}
+let gInspectee = null;
+let gWalker = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
     }).then(runNextTest));
   });
@@ -67,9 +61,8 @@ addTest(Task.async(function* testScrollIntoView() {
 }));
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gInspectee;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
   </script>
diff --git a/devtools/server/tests/mochitest/test_inspector-search-front.html b/devtools/server/tests/mochitest/test_inspector-search-front.html
index 807942b2d823..fc845a84b06d 100644
--- a/devtools/server/tests/mochitest/test_inspector-search-front.html
+++ b/devtools/server/tests/mochitest/test_inspector-search-front.html
@@ -10,17 +10,17 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=835896
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   const Cu = Components.utils;
   const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
   const promise = require("promise");
   const {InspectorFront} = require("devtools/shared/fronts/inspector");
-  const {console} = Cu.import("resource://gre/modules/Console.jsm", {});
 
   SimpleTest.waitForExplicitFinish();
 
   let walkerFront = null;
-  let inspectee = null;
   let inspector = null;
 
   // WalkerFront specific tests.  These aren't to excercise search
@@ -29,13 +29,13 @@ window.onload = function() {
   // See also test_inspector-search.html
 
   addAsyncTest(function* setup() {
-    info ("Setting up inspector and walker actors.");
+    info("Setting up inspector and walker actors.");
 
     let url = document.getElementById("inspectorContent").href;
 
+    // eslint-disable-next-line new-cap
     yield new promise(resolve => {
-      attachURL(url, function(err, client, tab, doc) {
-        inspectee = doc;
+      attachURL(url, function (err, client, tab, doc) {
         inspector = InspectorFront(client, tab);
         resolve();
       });
@@ -48,7 +48,7 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testWalkerFrontDefaults() {
-    info ("Testing search API using WalkerFront.");
+    info("Testing search API using WalkerFront.");
     let nodes = yield walkerFront.querySelectorAll(walkerFront.rootNode, "h2");
     let fronts = yield nodes.items();
 
@@ -77,7 +77,7 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testMultipleSearches() {
-    info ("Testing search API using WalkerFront (reverse=false)");
+    info("Testing search API using WalkerFront (reverse=false)");
     let nodes = yield walkerFront.querySelectorAll(walkerFront.rootNode, "h2");
     let fronts = yield nodes.items();
 
@@ -119,7 +119,7 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testMultipleSearchesReverse() {
-    info ("Testing search API using WalkerFront (reverse=true)");
+    info("Testing search API using WalkerFront (reverse=true)");
     let nodes = yield walkerFront.querySelectorAll(walkerFront.rootNode, "h2");
     let fronts = yield nodes.items();
 
@@ -168,9 +168,8 @@ window.onload = function() {
     runNextTest();
   });
 
-
   addAsyncTest(function* testBackwardsCompat() {
-    info ("Simulating a server that doesn't have the new search functionality.");
+    info("Simulating a server that doesn't have the new search functionality.");
     walkerFront.traits.textSearch = false;
     let front = yield walkerFront.querySelector(walkerFront.rootNode, "h1");
 
diff --git a/devtools/server/tests/mochitest/test_inspector-search.html b/devtools/server/tests/mochitest/test_inspector-search.html
index f5f2d0ef6344..1b6a6486758b 100644
--- a/devtools/server/tests/mochitest/test_inspector-search.html
+++ b/devtools/server/tests/mochitest/test_inspector-search.html
@@ -10,14 +10,15 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=835896
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   const Cu = Components.utils;
   const {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
   const promise = require("promise");
   const {InspectorFront} = require("devtools/shared/fronts/inspector");
   const {WalkerSearch, WalkerIndex} =
     require("devtools/server/actors/utils/walker-search");
-  const {console} = Cu.import("resource://gre/modules/Console.jsm", {});
 
   SimpleTest.waitForExplicitFinish();
 
@@ -31,12 +32,13 @@ window.onload = function() {
   // See also test_inspector-search-front.html.
 
   addAsyncTest(function* setup() {
-    info ("Setting up inspector and walker actors.");
+    info("Setting up inspector and walker actors.");
 
     let url = document.getElementById("inspectorContent").href;
 
+    // eslint-disable-next-line new-cap
     yield new promise(resolve => {
-      attachURL(url, function(err, client, tab, doc) {
+      attachURL(url, function (err, client, tab, doc) {
         inspectee = doc;
         inspector = InspectorFront(client, tab);
         resolve();
@@ -56,7 +58,7 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testIndexExists() {
-    info ("Testing basic index APIs exist.");
+    info("Testing basic index APIs exist.");
 
     let index = new WalkerIndex(walkerActor);
     ok(index.data.size > 0, "public index is filled after getting");
@@ -70,7 +72,7 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testSearchExists() {
-    info ("Testing basic search APIs exist.");
+    info("Testing basic search APIs exist.");
 
     ok(walkerSearch, "walker search exists on the WalkerActor");
     ok(walkerSearch.search, "walker search has `search` method");
@@ -88,8 +90,8 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testEmptySearch() {
-    info ("Testing search with an empty query.");
-    results = walkerSearch.search("");
+    info("Testing search with an empty query.");
+    let results = walkerSearch.search("");
     is(results.length, 0, "No results when searching for ''");
 
     results = walkerSearch.search(null);
@@ -165,7 +167,7 @@ window.onload = function() {
         {node: inspectee.querySelector("h1 + p > strong").childNodes[0], type: "text"},
       ]
     },
-    ]
+    ];
 
     for (let {desc, search, expected} of testData) {
       info("Running test: " + desc);
@@ -178,7 +180,7 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testPseudoElements() {
-    info ("Testing ::before and ::after element matching");
+    info("Testing ::before and ::after element matching");
 
     let beforeElt = new _documentWalker(inspectee.querySelector("#pseudo"),
                                         inspectee.defaultView).firstChild();
@@ -218,7 +220,7 @@ window.onload = function() {
   });
 
   addAsyncTest(function* testSearchMutationChangeResults() {
-    info ("Testing search before and after a mutation.");
+    info("Testing search before and after a mutation.");
     let expected = [
       {node: inspectee.querySelectorAll("h3")[0], type: "tag"},
       {node: inspectee.querySelectorAll("h3")[1], type: "tag"},
@@ -238,6 +240,7 @@ window.onload = function() {
       expected[2]
     ], "Results are updated after removal");
 
+    // eslint-disable-next-line new-cap
     yield new promise(resolve => {
       info("Waiting for a mutation to happen");
       let observer = new inspectee.defaultView.MutationObserver(() => {
@@ -254,6 +257,7 @@ window.onload = function() {
       expected[2]
     ], "Results are updated after addition");
 
+    // eslint-disable-next-line new-cap
     yield new promise(resolve => {
       info("Waiting for a mutation to happen");
       let observer = new inspectee.defaultView.MutationObserver(() => {
@@ -274,6 +278,7 @@ window.onload = function() {
   runNextTest();
 
   function mutateDocumentAndWaitForMutation(mutationFn) {
+    // eslint-disable-next-line new-cap
     return new promise(resolve => {
       info("Listening to markup mutation on the inspectee");
       let observer = new inspectee.defaultView.MutationObserver(resolve);
diff --git a/devtools/server/tests/mochitest/test_inspector-traversal.html b/devtools/server/tests/mochitest/test_inspector-traversal.html
index 2e1556717f93..590bd2f932de 100644
--- a/devtools/server/tests/mochitest/test_inspector-traversal.html
+++ b/devtools/server/tests/mochitest/test_inspector-traversal.html
@@ -11,24 +11,24 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/server/actors/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspectee = null;
-var gClient = null;
-var gWalker = null;
-var checkActorIDs = [];
+let gInspectee = null;
+let gClient = null;
+let gWalker = null;
+let checkActorIDs = [];
 
 function assertOwnership() {
   assertOwnershipTrees(gWalker);
 }
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
@@ -44,7 +44,8 @@ addTest(function testWalkerRoot() {
   // Make sure that refetching the root document of the walker returns the same
   // actor as the getWalker returned.
   promiseDone(gWalker.document().then(root => {
-    ok(root === gWalker.rootNode, "Re-fetching the document node should match the root document node.");
+    ok(root === gWalker.rootNode,
+       "Re-fetching the document node should match the root document node.");
     checkActorIDs.push(root.actorID);
     assertOwnership();
   }).then(runNextTest));
@@ -121,11 +122,12 @@ addTest(function testQuerySelectors() {
     is(nodes[0], firstNode, "First node should be reused.");
     ok(nodes[0]._parent, "Parent node should be set.");
     ok(nodes[0]._next || nodes[0]._prev, "Siblings should be set.");
-    ok(nodes[25]._next || nodes[25]._prev, "Siblings of " + nodes[25] + " should be set.");
+    ok(nodes[25]._next || nodes[25]._prev,
+       "Siblings of " + nodes[25] + " should be set.");
     assertOwnership();
     return nodeList.items(-1);
   }).then(nodes => {
-    is(nodes.length, 1, "Expect 1 node")
+    is(nodes.length, 1, "Expect 1 node");
     is(nodes[0].id, "z", "Expect it to be the last node.");
     checkActorIDs.push(nodes[0].actorID);
     // Save the node list ID so we can ensure it was destroyed.
@@ -142,17 +144,19 @@ addTest(function testQuerySelectors() {
 // Helper to check the response of requests that return hasFirst/hasLast/nodes
 // node lists (like `children` and `siblings`)
 function nodeArrayChecker(first, last, ids) {
-  return function(response) {
-    is(response.hasFirst, first, "Should " + (first ? "" : "not ") + " have the first node.");
+  return function (response) {
+    is(response.hasFirst, first,
+       "Should " + (first ? "" : "not ") + " have the first node.");
     is(response.hasLast, last, "Should " + (last ? "" : "not ") + " have the last node.");
-    is(response.nodes.length, ids.length, "Should have " + ids.length + " children listed.");
-    let responseIds = '';
-    for (node of response.nodes) {
+    is(response.nodes.length, ids.length,
+       "Should have " + ids.length + " children listed.");
+    let responseIds = "";
+    for (let node of response.nodes) {
       responseIds += node.id;
     }
     is(responseIds, ids, "Correct nodes were returned.");
     assertOwnership();
-  }
+  };
 }
 
 addTest(function testNoChildren() {
@@ -163,8 +167,8 @@ addTest(function testNoChildren() {
 });
 
 addTest(function testLongListTraversal() {
-  var longList;
-  var allChildren;
+  let longList;
+  let allChildren;
   promiseDone(gWalker.querySelector(gWalker.rootNode, "#longlist").then(node => {
     longList = node;
     // First call with no options, expect all children.
@@ -177,36 +181,37 @@ addTest(function testLongListTraversal() {
   }).then(() => {
     // maxNodes should limit us to the first 5 nodes.
     assertOwnership();
-    return gWalker.children(longList, { maxNodes: 5 }).then(nodeArrayChecker(true, false, 'abcde'));
+    return gWalker.children(longList, { maxNodes: 5 })
+           .then(nodeArrayChecker(true, false, "abcde"));
   }).then(() => {
     assertOwnership();
     // maxNodes with the second item centered should still give us the first 5 nodes.
     return gWalker.children(longList, { maxNodes: 5, center: allChildren[1] }).then(
-      nodeArrayChecker(true, false, 'abcde')
+      nodeArrayChecker(true, false, "abcde")
     );
   }).then(() => {
     // maxNodes with a center in the middle of the list should put that item in the middle
     let center = allChildren[13];
-    is(center.id, 'n', "Make sure I know how to count letters.");
+    is(center.id, "n", "Make sure I know how to count letters.");
     return gWalker.children(longList, { maxNodes: 5, center: center }).then(
-      nodeArrayChecker(false, false, 'lmnop')
+      nodeArrayChecker(false, false, "lmnop")
     );
   }).then(() => {
     // maxNodes with the second-to-last item centered should give us the last 5 nodes.
     return gWalker.children(longList, { maxNodes: 5, center: allChildren[24] }).then(
-      nodeArrayChecker(false, true, 'vwxyz')
+      nodeArrayChecker(false, true, "vwxyz")
     );
   }).then(() => {
     // maxNodes with a start in the middle should start at that node and fetch 5
     let start = allChildren[13];
-    is(start.id, 'n', "Make sure I know how to count letters.")
+    is(start.id, "n", "Make sure I know how to count letters.");
     return gWalker.children(longList, { maxNodes: 5, start: start }).then(
-      nodeArrayChecker(false, false, 'nopqr')
+      nodeArrayChecker(false, false, "nopqr")
     );
   }).then(() => {
     // maxNodes near the end should only return what's left
     return gWalker.children(longList, { maxNodes: 5, start: allChildren[24] }).then(
-      nodeArrayChecker(false, true, 'yz')
+      nodeArrayChecker(false, true, "yz")
     );
   }).then(runNextTest));
 });
@@ -221,7 +226,8 @@ addTest(function testObjectNodeChildren() {
 
 addTest(function testSiblings() {
   promiseDone(gWalker.querySelector(gWalker.rootNode, "#a").then(a => {
-    return gWalker.siblings(a, { maxNodes: 5, center: a }).then(nodeArrayChecker(true, false, "abcde"));
+    return gWalker.siblings(a, { maxNodes: 5, center: a })
+           .then(nodeArrayChecker(true, false, "abcde"));
   }).then(() => {
     return gWalker.siblings(gWalker.rootNode).then(response => {
       ok(response.hasFirst && response.hasLast, "Has first and last.");
@@ -255,7 +261,6 @@ addTest(function testPreviousSibling() {
   }).then(runNextTest));
 });
 
-
 addTest(function testFrameTraversal() {
   promiseDone(gWalker.querySelector(gWalker.rootNode, "#childFrame").then(childFrame => {
     return gWalker.children(childFrame);
@@ -268,7 +273,8 @@ addTest(function testFrameTraversal() {
     return gWalker.parents(childDocumentZ);
   }).then(parents => {
     // Expected set of parent tag names for this item:
-    let expectedParents = ['DIV', 'BODY', 'HTML', '#document', 'IFRAME', 'BODY', 'HTML', '#document'];
+    let expectedParents = ["DIV", "BODY", "HTML", "#document", "IFRAME", "BODY", "HTML",
+                           "#document"];
     for (let parent of parents) {
       let expected = expectedParents.shift();
       is(parent.nodeName, expected, "Got expected parent");
@@ -278,8 +284,10 @@ addTest(function testFrameTraversal() {
 
 addTest(function testLongValue() {
   const testSummaryLength = 10;
+  const inspector = require("devtools/server/actors/inspector");
+
   inspector.setValueSummaryLength(testSummaryLength);
-  SimpleTest.registerCleanupFunction(function() {
+  SimpleTest.registerCleanupFunction(function () {
     inspector.setValueSummaryLength(inspector.DEFAULT_VALUE_SUMMARY_LENGTH);
   });
 
@@ -298,7 +306,8 @@ addTest(function testLongValue() {
   }).then(value => {
     return value.string();
   }).then(valueStr => {
-    is(valueStr, longstringText, "Full node value should match the string from the document.");
+    is(valueStr, longstringText,
+       "Full node value should match the string from the document.");
   }).then(runNextTest));
 });
 
@@ -318,7 +327,8 @@ addTest(function testShortValue() {
   }).then(value => {
     return value.string();
   }).then(valueStr => {
-    is(valueStr, shortstringText, "Full node value should match the string from the document.");
+    is(valueStr, shortstringText,
+       "Full node value should match the string from the document.");
   }).then(runNextTest));
 });
 
@@ -327,18 +337,16 @@ addTest(function testReleaseWalker() {
 
   promiseDone(gWalker.release().then(() => {
     let promises = Array.from(checkActorIDs, (id) => checkMissing(gClient, id));
-    return promise.all(promises)
+    return promise.all(promises);
   }).then(runNextTest));
 });
 
 addTest(function cleanup() {
-  delete gWalker;
-  delete gInspectee;
-  delete gClient;
+  gWalker = null;
+  gInspectee = null;
+  gClient = null;
   runNextTest();
 });
-
-
   </script>
 </head>
 <body>
diff --git a/devtools/server/tests/mochitest/test_inspector_getImageData-wait-for-load.html b/devtools/server/tests/mochitest/test_inspector_getImageData-wait-for-load.html
index 58d92573efac..120a3996cd65 100644
--- a/devtools/server/tests/mochitest/test_inspector_getImageData-wait-for-load.html
+++ b/devtools/server/tests/mochitest/test_inspector_getImageData-wait-for-load.html
@@ -17,10 +17,13 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1192536
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
+"use strict";
 
 const flags = require("devtools/shared/flags");
 const wasTesting = flags.testing;
-SimpleTest.registerCleanupFunction(() => flags.testing = wasTesting);
+SimpleTest.registerCleanupFunction(function () {
+  flags.testing = wasTesting;
+});
 
 const PATH = "http://mochi.test:8888/chrome/devtools/server/tests/mochitest/";
 const BASE_IMAGE = PATH + "inspector-delay-image-response.sjs";
@@ -28,23 +31,24 @@ const DELAYED_IMAGE = BASE_IMAGE + "?delay=300";
 const TIMEOUT_IMAGE = BASE_IMAGE + "?delay=50000";
 const NONEXISTENT_IMAGE = PATH + "this-does-not-exist.png";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gImg = null;
-var gNodeFront = null;
-var gWalker = null;
+let gImg = null;
+let gNodeFront = null;
+let gWalker = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
 
     promiseDone(inspector.getWalker().then(walker => {
       gWalker = walker;
+      // eslint-disable-next-line max-nested-callbacks
       return walker.querySelector(gWalker.rootNode, "img.custom").then(img => {
         gNodeFront = img;
         gImg = doc.querySelector("img.custom");
@@ -93,9 +97,9 @@ addTest(function testDelayedImage() {
 });
 
 addTest(function cleanup() {
-  delete gImg;
-  delete gNodeFront
-  delete gWalker;
+  gImg = null;
+  gNodeFront = null;
+  gWalker = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_inspector_getImageData.html b/devtools/server/tests/mochitest/test_inspector_getImageData.html
index a73d8b64734d..e2acea1bbc76 100644
--- a/devtools/server/tests/mochitest/test_inspector_getImageData.html
+++ b/devtools/server/tests/mochitest/test_inspector_getImageData.html
@@ -11,18 +11,18 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=932937
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
+let gWalker = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
 
@@ -45,6 +45,7 @@ addTest(function testLargeImage() {
       is(imageData.size.naturalHeight, 3000, "Natural width of the image correct");
       ok(imageData.size.resized, "Image was resized");
 
+      // eslint-disable-next-line max-nested-callbacks
       imageData.data.string().then(str => {
         ok(str, "We have an image data string!");
         testResizing(imageData, str);
@@ -66,6 +67,7 @@ addTest(function testLargeCanvas() {
       is(imageData.size.naturalHeight, 2000, "Natural width of the image correct");
       ok(imageData.size.resized, "Image was resized");
 
+      // eslint-disable-next-line max-nested-callbacks
       imageData.data.string().then(str => {
         ok(str, "We have an image data string!");
         testResizing(imageData, str);
@@ -87,6 +89,7 @@ addTest(function testSmallImage() {
       is(imageData.size.naturalHeight, 240, "Natural width of the image correct");
       ok(!imageData.size.resized, "Image was NOT resized");
 
+      // eslint-disable-next-line max-nested-callbacks
       imageData.data.string().then(str => {
         ok(str, "We have an image data string!");
         testResizing(imageData, str);
@@ -108,6 +111,7 @@ addTest(function testDataImage() {
       is(imageData.size.naturalHeight, 28, "Natural width of the image correct");
       ok(imageData.size.resized, "Image was resized");
 
+      // eslint-disable-next-line max-nested-callbacks
       imageData.data.string().then(str => {
         ok(str, "We have an image data string!");
         testResizing(imageData, str);
@@ -123,7 +127,7 @@ addTest(function testNonImgOrCanvasElements() {
 });
 
 addTest(function cleanup() {
-  delete gWalker;
+  gWalker = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_inspector_getImageDataFromURL.html b/devtools/server/tests/mochitest/test_inspector_getImageDataFromURL.html
index 91a0da5f3d1c..e091fa83f962 100644
--- a/devtools/server/tests/mochitest/test_inspector_getImageDataFromURL.html
+++ b/devtools/server/tests/mochitest/test_inspector_getImageDataFromURL.html
@@ -16,10 +16,13 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1192536
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
+"use strict";
 
 const flags = require("devtools/shared/flags");
 const wasTesting = flags.testing;
-SimpleTest.registerCleanupFunction(() => flags.testing = wasTesting);
+SimpleTest.registerCleanupFunction(function () {
+  flags.testing = wasTesting;
+});
 
 const PATH = "http://mochi.test:8888/chrome/devtools/server/tests/mochitest/";
 const BASE_IMAGE = PATH + "inspector-delay-image-response.sjs";
@@ -27,16 +30,16 @@ const DELAYED_IMAGE = BASE_IMAGE + "?delay=300";
 const TIMEOUT_IMAGE = BASE_IMAGE + "?delay=50000";
 const NONEXISTENT_IMAGE = PATH + "this-does-not-exist.png";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gInspector = null;
+let gInspector = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     gInspector = InspectorFront(client, tab);
     runNextTest();
@@ -73,7 +76,7 @@ addTest(function testNormalImage() {
 });
 
 addTest(function cleanup() {
-  delete gInspector;
+  gInspector = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_inspector_getNodeFromActor.html b/devtools/server/tests/mochitest/test_inspector_getNodeFromActor.html
index e2f342e2b8da..d57ab54fc7fc 100644
--- a/devtools/server/tests/mochitest/test_inspector_getNodeFromActor.html
+++ b/devtools/server/tests/mochitest/test_inspector_getNodeFromActor.html
@@ -11,18 +11,18 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1155653
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/shared/fronts/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker;
+let gWalker;
 
-addTest(function() {
+addTest(function () {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
 
@@ -32,7 +32,7 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   info("Try to get a NodeFront from an invalid actorID");
   gWalker.getNodeFromActor("invalid", ["node"]).then(node => {
     ok(!node, "The node returned is null");
@@ -40,7 +40,7 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   info("Try to get a NodeFront from a valid actorID but invalid path");
   gWalker.getNodeFromActor(gWalker.actorID, ["invalid", "path"]).then(node => {
     ok(!node, "The node returned is null");
@@ -48,7 +48,7 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   info("Try to get a NodeFront from a valid actorID and valid path");
   gWalker.getNodeFromActor(gWalker.actorID, ["rootDoc"]).then(rootDocNode => {
     ok(rootDocNode, "A node was returned");
@@ -57,19 +57,19 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   info("Try to get a NodeFront from a valid actorID and valid complex path");
   gWalker.getNodeFromActor(gWalker.actorID,
     ["tabActor", "window", "document", "body"]).then(bodyNode => {
-    ok(bodyNode, "A node was returned");
-    gWalker.querySelector(gWalker.rootNode, "body").then(node => {
-      is(bodyNode, node, "The body node was returned");
-      runNextTest();
+      ok(bodyNode, "A node was returned");
+      gWalker.querySelector(gWalker.rootNode, "body").then(node => {
+        is(bodyNode, node, "The body node was returned");
+        runNextTest();
+      });
     });
-  });
 });
 
-addTest(function() {
+addTest(function () {
   gWalker = null;
   runNextTest();
 });
diff --git a/devtools/server/tests/mochitest/test_makeGlobalObjectReference.html b/devtools/server/tests/mochitest/test_makeGlobalObjectReference.html
index 8bd7e0476b50..250149b6faf7 100644
--- a/devtools/server/tests/mochitest/test_makeGlobalObjectReference.html
+++ b/devtools/server/tests/mochitest/test_makeGlobalObjectReference.html
@@ -15,6 +15,7 @@ Debugger.prototype.makeGlobalObjectReference should dereference WindowProxy
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 Components.utils.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
@@ -22,23 +23,27 @@ addDebuggerToGlobal(this);
 window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var iframe = document.createElement("iframe");
-  iframe.src = "data:text/html,<html>The word 'smorgasbord', spoken by an adorably plump child, symbolizing prosperity</html>";
+  let iframe = document.createElement("iframe");
+  iframe.src = "data:text/html,<html>The word 'smorgasbord'," +
+               " spoken by an adorably plump child, symbolizing prosperity</html>";
   iframe.onload = iframeOnLoad;
   document.body.appendChild(iframe);
 
   function iframeOnLoad() {
-    var dbg = new Debugger;
+    let dbg = new Debugger();
 
-    var g1o = iframe.contentWindow; // 'o' for 'outer window'
+    // 'o' for 'outer window'
+    let g1o = iframe.contentWindow;
     ok(!dbg.hasDebuggee(g1o), "iframe is not initially a debuggee");
 
     // Like addDebuggee, makeGlobalObjectReference innerizes.
     // 'i' stands for 'inner window'.
     // 'DO' stands for 'Debugger.Object'.
-    var g1iDO = dbg.makeGlobalObjectReference(g1o);
-    ok(!dbg.hasDebuggee(g1o), "makeGlobalObjectReference does not add g1 as debuggee, designated via outer");
-    ok(!dbg.hasDebuggee(g1iDO), "makeGlobalObjectReference does not add g1 as debuggee, designated via D.O ");
+    let g1iDO = dbg.makeGlobalObjectReference(g1o);
+    ok(!dbg.hasDebuggee(g1o),
+       "makeGlobalObjectReference does not add g1 as debuggee, designated via outer");
+    ok(!dbg.hasDebuggee(g1iDO),
+       "makeGlobalObjectReference does not add g1 as debuggee, designated via D.O ");
 
     // Wrapping an object automatically outerizes it, so dereferencing an
     // inner object D.O gets you an outer object.
@@ -47,28 +52,32 @@ window.onload = function () {
     ok(g1iDO.unsafeDereference() === g1o, "g1iDO has the right referent");
 
     // However, Debugger.Objects do distinguish inner and outer windows.
-    var g1oDO = g1iDO.makeDebuggeeValue(g1o);
+    let g1oDO = g1iDO.makeDebuggeeValue(g1o);
     ok(g1iDO !== g1oDO, "makeDebuggeeValue doesn't innerize");
     ok(g1iDO.unsafeDereference() === g1oDO.unsafeDereference(),
-       "unsafeDereference() outerizes, so inner and outer window D.Os both dereference to outer");
+       "unsafeDereference() outerizes," +
+       " so inner and outer window D.Os both dereference to outer");
 
     ok(dbg.addDebuggee(g1o) === g1iDO, "addDebuggee returns the inner window's D.O");
     ok(dbg.hasDebuggee(g1o), "addDebuggee adds the correct global");
-    ok(dbg.hasDebuggee(g1iDO), "hasDebuggee can take a D.O referring to the inner window");
-    ok(dbg.hasDebuggee(g1oDO), "hasDebuggee can take a D.O referring to the outer window");
+    ok(dbg.hasDebuggee(g1iDO),
+       "hasDebuggee can take a D.O referring to the inner window");
+    ok(dbg.hasDebuggee(g1oDO),
+       "hasDebuggee can take a D.O referring to the outer window");
 
-    var iframe2 = document.createElement("iframe");
-    iframe2.src = "data:text/html,<html>Her retrospection, in hindsight, was prescient.</html>";
+    let iframe2 = document.createElement("iframe");
+    iframe2.src = "data:text/html,<html>Her retrospection," +
+                  " in hindsight, was prescient.</html>";
     iframe2.onload = iframe2OnLoad;
     document.body.appendChild(iframe2);
 
     function iframe2OnLoad() {
       // makeGlobalObjectReference dereferences CCWs.
-      var g2o = iframe2.contentWindow;
+      let g2o = iframe2.contentWindow;
       g2o.g1o = g1o;
 
-      var g2iDO = dbg.addDebuggee(g2o);
-      var g2g1oDO = g2iDO.getOwnPropertyDescriptor('g1o').value;
+      let g2iDO = dbg.addDebuggee(g2o);
+      let g2g1oDO = g2iDO.getOwnPropertyDescriptor("g1o").value;
       ok(g2g1oDO !== g1oDO, "g2's cross-compartment wrapper for g1o gets its own D.O");
       ok(g2g1oDO.unwrap() === g1oDO,
          "unwrapping g2's cross-compartment wrapper for g1o gets the right D.O");
@@ -78,7 +87,7 @@ window.onload = function () {
       SimpleTest.finish();
     }
   }
-}
+};
 
 </script>
 </pre>
diff --git a/devtools/server/tests/mochitest/test_memory.html b/devtools/server/tests/mochitest/test_memory.html
index ba929105c51c..d5e8b21f328a 100644
--- a/devtools/server/tests/mochitest/test_memory.html
+++ b/devtools/server/tests/mochitest/test_memory.html
@@ -13,12 +13,14 @@ Bug 923275 - Add a memory monitor widget to the developer toolbar
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
-    var measurement = yield memory.measure();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let measurement = yield memory.measure();
     ok(measurement.total > 0, "total memory is valid");
     ok(measurement.domSize > 0, "domSize is valid");
     ok(measurement.styleSize > 0, "styleSize is valid");
diff --git a/devtools/server/tests/mochitest/test_memory_allocations_01.html b/devtools/server/tests/mochitest/test_memory_allocations_01.html
index dbc2d190f7aa..bbf20ae8f1fb 100644
--- a/devtools/server/tests/mochitest/test_memory_allocations_01.html
+++ b/devtools/server/tests/mochitest/test_memory_allocations_01.html
@@ -13,11 +13,13 @@ Bug 1067491 - Test recording allocations.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
     yield memory.startRecordingAllocations();
@@ -25,18 +27,22 @@ window.onload = function() {
 
     // Allocate some objects.
 
-    var alloc1, alloc2, alloc3;
+    let alloc1, alloc2, alloc3;
+
+    /* eslint-disable max-nested-callbacks */
     (function outer() {
       (function middle() {
         (function inner() {
-          alloc1 = {};                alloc1.line = Error().lineNumber;
-          alloc2 = [];                alloc2.line = Error().lineNumber;
-          alloc3 = new function() {}; alloc3.line = Error().lineNumber;
+          alloc1 = {}; alloc1.line = Error().lineNumber;
+          alloc2 = []; alloc2.line = Error().lineNumber;
+          // eslint-disable-next-line new-parens
+          alloc3 = new function () {}; alloc3.line = Error().lineNumber;
         }());
       }());
     }());
+    /* eslint-enable max-nested-callbacks */
 
-    var response = yield memory.getAllocations();
+    let response = yield memory.getAllocations();
 
     yield memory.stopRecordingAllocations();
     ok(true, "Can stop recording allocations");
@@ -45,7 +51,7 @@ window.onload = function() {
     // allocations that occurred in our test case above.
 
     function isTestAllocation(alloc) {
-      var frame = response.frames[alloc];
+      let frame = response.frames[alloc];
       return frame
         && frame.functionDisplayName === "inner"
         && (frame.line === alloc1.line
@@ -53,7 +59,7 @@ window.onload = function() {
             || frame.line === alloc3.line);
     }
 
-    var testAllocations = response.allocations.filter(isTestAllocation);
+    let testAllocations = response.allocations.filter(isTestAllocation);
     ok(testAllocations.length >= 3,
        "Should find our 3 test allocations (plus some allocations for the error "
        + "objects used to get line numbers)");
@@ -63,19 +69,19 @@ window.onload = function() {
     // line we expected (rather than a bunch on the first line and none on the
     // others, etc).
 
-    var expectedLines = new Set([alloc1.line, alloc2.line, alloc3.line]);
+    let expectedLines = new Set([alloc1.line, alloc2.line, alloc3.line]);
 
-    for (var alloc of testAllocations) {
-      var innerFrame = response.frames[alloc];
+    for (let alloc of testAllocations) {
+      let innerFrame = response.frames[alloc];
       ok(innerFrame, "Should get the inner frame");
       is(innerFrame.functionDisplayName, "inner");
       expectedLines.delete(innerFrame.line);
 
-      var middleFrame = response.frames[innerFrame.parent];
+      let middleFrame = response.frames[innerFrame.parent];
       ok(middleFrame, "Should get the middle frame");
       is(middleFrame.functionDisplayName, "middle");
 
-      var outerFrame = response.frames[middleFrame.parent];
+      let outerFrame = response.frames[middleFrame.parent];
       ok(outerFrame, "Should get the outer frame");
       is(outerFrame.functionDisplayName, "outer");
 
diff --git a/devtools/server/tests/mochitest/test_memory_allocations_02.html b/devtools/server/tests/mochitest/test_memory_allocations_02.html
index 1d35d7207cef..40b9e3c6dac0 100644
--- a/devtools/server/tests/mochitest/test_memory_allocations_02.html
+++ b/devtools/server/tests/mochitest/test_memory_allocations_02.html
@@ -13,27 +13,29 @@ Bug 1132764 - Test controlling the maximum allocations log length over the RDP.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
-    var allocs = [];
-    var eventsFired = 0;
-    var intervalId = null;
-    function onAlloc () {
+    let allocs = [];
+    let eventsFired = 0;
+    let intervalId = null;
+    function onAlloc() {
       eventsFired++;
     }
-    function startAllocating () {
+    function startAllocating() {
       intervalId = setInterval(() => {
-        for (var i = 100000; --i;) {
+        for (let i = 100000; --i;) {
           allocs.push(new Object());
         }
       }, 1);
     }
-    function stopAllocating () {
+    function stopAllocating() {
       clearInterval(intervalId);
     }
 
@@ -44,14 +46,15 @@ window.onload = function() {
     });
 
     yield waitUntil(() => eventsFired > 5);
-    ok(eventsFired > 5, "Some allocation events fired without allocating much via auto drain");
+    ok(eventsFired > 5,
+       "Some allocation events fired without allocating much via auto drain");
     yield memory.stopRecordingAllocations();
 
     // Set a really high auto drain timer so we can test if
     // it fires on GC
     eventsFired = 0;
-    var startTime = performance.now();
-    var drainTimer = 1000000;
+    let startTime = performance.now();
+    let drainTimer = 1000000;
     yield memory.startRecordingAllocations({
       drainAllocationsTimeout: drainTimer
     });
@@ -62,7 +65,8 @@ window.onload = function() {
       return eventsFired > 1;
     });
     stopAllocating();
-    ok(performance.now() - drainTimer < startTime, "Allocation events fired on GC before timer");
+    ok(performance.now() - drainTimer < startTime,
+       "Allocation events fired on GC before timer");
     yield memory.stopRecordingAllocations();
 
     memory.off("allocations", onAlloc);
diff --git a/devtools/server/tests/mochitest/test_memory_allocations_03.html b/devtools/server/tests/mochitest/test_memory_allocations_03.html
index 6420746c5ec8..89dc7a610e79 100644
--- a/devtools/server/tests/mochitest/test_memory_allocations_03.html
+++ b/devtools/server/tests/mochitest/test_memory_allocations_03.html
@@ -13,11 +13,13 @@ Bug 1067491 - Test that frames keep the same index while we are recording.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
     yield memory.startRecordingAllocations();
@@ -26,18 +28,18 @@ window.onload = function() {
     // allocating directly in the generator), but with getAllocations() calls in
     // between.
 
-    var allocs = [];
+    let allocs = [];
     function allocator() {
       allocs.push({});
     }
 
     setTimeout(allocator, 1);
     yield waitForTime(2);
-    var first = yield memory.getAllocations();
+    let first = yield memory.getAllocations();
 
     setTimeout(allocator, 1);
     yield waitForTime(2);
-    var second = yield memory.getAllocations();
+    let second = yield memory.getAllocations();
 
     yield memory.stopRecordingAllocations();
 
@@ -48,7 +50,6 @@ window.onload = function() {
     // but before the second.
 
     function assertSameFrame(a, b) {
-      info("Checking frames at index " + i + ":");
       info("  First frame = " + JSON.stringify(a, null, 4));
       info("  Second frame = " + JSON.stringify(b, null, 4));
 
@@ -64,7 +65,8 @@ window.onload = function() {
       is(a.parent, b.parent);
     }
 
-    for (var i = 0; i < first.frames.length; i++) {
+    for (let i = 0; i < first.frames.length; i++) {
+      info("Checking frames at index " + i + ":");
       assertSameFrame(first.frames[i], second.frames[i]);
     }
 
diff --git a/devtools/server/tests/mochitest/test_memory_allocations_04.html b/devtools/server/tests/mochitest/test_memory_allocations_04.html
index 16a267621a20..4c1eb60b7468 100644
--- a/devtools/server/tests/mochitest/test_memory_allocations_04.html
+++ b/devtools/server/tests/mochitest/test_memory_allocations_04.html
@@ -13,27 +13,29 @@ Bug 1068171 - Test controlling the memory actor's allocation sampling probabilit
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
-    var allocs = [];
+    let allocs = [];
     function allocator() {
-      for (var i = 0; i < 100; i++) {
+      for (let i = 0; i < 100; i++) {
         allocs.push({});
       }
     }
 
-    var testProbability = Task.async(function* (p, expected) {
+    let testProbability = Task.async(function* (p, expected) {
       info("probability = " + p);
       yield memory.startRecordingAllocations({
         probability: p
       });
       allocator();
-      var response = yield memory.getAllocations();
+      let response = yield memory.getAllocations();
       yield memory.stopRecordingAllocations();
       return response.allocations.length;
     });
diff --git a/devtools/server/tests/mochitest/test_memory_allocations_05.html b/devtools/server/tests/mochitest/test_memory_allocations_05.html
index e9452b8d3d4d..1eea45a4b67f 100644
--- a/devtools/server/tests/mochitest/test_memory_allocations_05.html
+++ b/devtools/server/tests/mochitest/test_memory_allocations_05.html
@@ -13,24 +13,27 @@ Bug 1068144 - Test getting the timestamps for allocations.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
-    var allocs = [];
+    let allocs = [];
     function allocator() {
-      allocs.push(new Object);
+      allocs.push(new Object());
     }
 
     // Using setTimeout results in wildly varying delays that make it hard to
     // test our timestamps and results in intermittent failures. Instead, we
     // actually spin an empty loop for a whole millisecond.
     function actuallyWaitOneWholeMillisecond() {
-      var start = window.performance.now();
-      while (window.performance.now() - start < 1.000) ;
+      let start = window.performance.now();
+      // eslint-disable-next-line curly
+      while (window.performance.now() - start < 1.000);
     }
 
     yield memory.startRecordingAllocations();
@@ -41,36 +44,39 @@ window.onload = function() {
     actuallyWaitOneWholeMillisecond();
     allocator();
 
-    var response = yield memory.getAllocations();
+    let response = yield memory.getAllocations();
     yield memory.stopRecordingAllocations();
 
     ok(response.allocationsTimestamps, "The response should have timestamps.");
     is(response.allocationsTimestamps.length, response.allocations.length,
        "There should be a timestamp for every allocation.");
 
-    var allocatorIndices = response.allocations
+    let allocatorIndices = response.allocations
       .map(function (a, idx) {
-        var frame = response.frames[a];
+        let frame = response.frames[a];
         if (frame && frame.functionDisplayName === "allocator") {
           return idx;
         }
+        return null;
       })
       .filter(function (idx) {
-        return idx !== undefined;
+        return idx !== null;
       });
 
-    is(allocatorIndices.length, 3, "Should have our 3 allocations from the `allocator` timeouts.");
+    is(allocatorIndices.length, 3,
+       "Should have our 3 allocations from the `allocator` timeouts.");
 
-    var lastTimestamp;
-    for (var i = 0; i < 3; i++) {
-      var timestamp = response.allocationsTimestamps[allocatorIndices[i]];
+    let lastTimestamp;
+    for (let i = 0; i < 3; i++) {
+      let timestamp = response.allocationsTimestamps[allocatorIndices[i]];
       info("timestamp", timestamp);
       ok(timestamp, "We should have a timestamp for the `allocator` allocation.");
 
       if (lastTimestamp) {
-        var delta = timestamp - lastTimestamp;
+        let delta = timestamp - lastTimestamp;
         info("delta since last timestamp", delta);
-        ok(delta >= 1 /* ms */,
+        // ms
+        ok(delta >= 1,
            "The timestamp should be about 1 ms after the last timestamp.");
       }
 
diff --git a/devtools/server/tests/mochitest/test_memory_allocations_06.html b/devtools/server/tests/mochitest/test_memory_allocations_06.html
index 24d564b3915d..b9b19744fcba 100644
--- a/devtools/server/tests/mochitest/test_memory_allocations_06.html
+++ b/devtools/server/tests/mochitest/test_memory_allocations_06.html
@@ -13,16 +13,18 @@ Bug 1132764 - Test controlling the maximum allocations log length over the RDP.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
-    var allocs = [];
+    let allocs = [];
     function allocator() {
-      allocs.push(new Object);
+      allocs.push(new Object());
     }
 
     yield memory.startRecordingAllocations({
@@ -33,7 +35,7 @@ window.onload = function() {
     allocator();
     allocator();
 
-    var response = yield memory.getAllocations();
+    let response = yield memory.getAllocations();
     yield memory.stopRecordingAllocations();
 
     is(response.allocations.length, 1,
diff --git a/devtools/server/tests/mochitest/test_memory_allocations_07.html b/devtools/server/tests/mochitest/test_memory_allocations_07.html
index cfa051d3a68f..9cf4a6c30295 100644
--- a/devtools/server/tests/mochitest/test_memory_allocations_07.html
+++ b/devtools/server/tests/mochitest/test_memory_allocations_07.html
@@ -13,16 +13,18 @@ Bug 1192335 - Test getting the byte sizes for allocations.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
-    var allocs = [];
+    let allocs = [];
     function allocator() {
-      allocs.push(new Object);
+      allocs.push(new Object());
     }
 
     yield memory.startRecordingAllocations();
@@ -31,7 +33,7 @@ window.onload = function() {
     allocator();
     allocator();
 
-    var response = yield memory.getAllocations();
+    let response = yield memory.getAllocations();
     yield memory.stopRecordingAllocations();
 
     ok(response.allocationSizes, "The response should have bytesizes.");
@@ -39,14 +41,15 @@ window.onload = function() {
        "There should be a bytesize for every allocation.");
     ok(response.allocationSizes.length >= 3,
        "There are atleast 3 allocations.");
-    ok(response.allocationSizes.every(isPositiveNumber), "every bytesize is a positive number");
+    ok(response.allocationSizes.every(isPositiveNumber),
+       "every bytesize is a positive number");
 
     yield memory.detach();
     destroyServerAndFinish(client);
   });
 };
 
-function isPositiveNumber (n) {
+function isPositiveNumber(n) {
   return typeof n === "number" && n > 0;
 }
 </script>
diff --git a/devtools/server/tests/mochitest/test_memory_attach_01.html b/devtools/server/tests/mochitest/test_memory_attach_01.html
index 2e46f60282ef..3d0187d5ed69 100644
--- a/devtools/server/tests/mochitest/test_memory_attach_01.html
+++ b/devtools/server/tests/mochitest/test_memory_attach_01.html
@@ -13,16 +13,18 @@ Bug 960671 - Test attaching and detaching from a memory actor.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
     ok(true, "Shouldn't have gotten an error attaching.");
     yield memory.detach();
     ok(true, "Shouldn't have gotten an error detaching.");
-   destroyServerAndFinish(client);
+    destroyServerAndFinish(client);
   });
 };
 </script>
diff --git a/devtools/server/tests/mochitest/test_memory_attach_02.html b/devtools/server/tests/mochitest/test_memory_attach_02.html
index 790290743c8f..f79d66c0a91b 100644
--- a/devtools/server/tests/mochitest/test_memory_attach_02.html
+++ b/devtools/server/tests/mochitest/test_memory_attach_02.html
@@ -13,17 +13,18 @@ Bug 960671 - Test attaching and detaching while in the wrong state.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
 
-    var e = null;
+    let e = null;
     try {
       yield memory.detach();
-    }
-    catch (ee) {
+    } catch (ee) {
       e = ee;
     }
     ok(e, "Should have hit the wrongState error");
@@ -33,8 +34,7 @@ window.onload = function() {
     e = null;
     try {
       yield memory.attach();
-    }
-    catch (ee) {
+    } catch (ee) {
       e = ee;
     }
     ok(e, "Should have hit the wrongState error");
diff --git a/devtools/server/tests/mochitest/test_memory_census.html b/devtools/server/tests/mochitest/test_memory_census.html
index 783fc139a2e2..209f1bbf2dd5 100644
--- a/devtools/server/tests/mochitest/test_memory_census.html
+++ b/devtools/server/tests/mochitest/test_memory_census.html
@@ -13,14 +13,16 @@ Bug 1067491 - Test taking a census over the RDP.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
-    var census = yield memory.takeCensus();
+    let census = yield memory.takeCensus();
     is(typeof census, "object");
 
     yield memory.detach();
diff --git a/devtools/server/tests/mochitest/test_memory_gc_01.html b/devtools/server/tests/mochitest/test_memory_gc_01.html
index bc979c630894..2f894d03777a 100644
--- a/devtools/server/tests/mochitest/test_memory_gc_01.html
+++ b/devtools/server/tests/mochitest/test_memory_gc_01.html
@@ -13,27 +13,31 @@ Bug 1067491 - Test forcing a gc.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
+
+    let beforeGC, afterGC;
 
     do {
-      var objects = [];
-      for (var i = 0; i < 1000; i++) {
-        var o = {};
+      let objects = [];
+      for (let i = 0; i < 1000; i++) {
+        let o = {};
         o[Math.random()] = 1;
         objects.push(o);
       }
-
       objects = null;
 
-      var { total: beforeGC } = yield memory.measure();
+      yield { total: beforeGC } = memory.measure();
 
       yield memory.forceGarbageCollection();
-      var { total: afterGC } = yield memory.measure();
-    } while(beforeGC < afterGC);
+
+      yield { total: afterGC } = memory.measure();
+    } while (beforeGC < afterGC);
 
     ok(true, "The amount of memory after GC should eventually decrease");
 
diff --git a/devtools/server/tests/mochitest/test_memory_gc_events.html b/devtools/server/tests/mochitest/test_memory_gc_events.html
index cf8dae53e356..99c292d60431 100644
--- a/devtools/server/tests/mochitest/test_memory_gc_events.html
+++ b/devtools/server/tests/mochitest/test_memory_gc_events.html
@@ -13,16 +13,18 @@ Bug 1137527 - Test receiving GC events from the memory actor.
 <pre id="test">
 <script src="memory-helpers.js" type="application/javascript"></script>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var event = require("sdk/event/core");
+  let event = require("sdk/event/core");
 
   Task.spawn(function* () {
-    var { memory, client } = yield startServerAndGetSelectedTabMemory();
+    let { memory, client } = yield startServerAndGetSelectedTabMemory();
     yield memory.attach();
 
-    var gotGcEvent = new Promise(resolve => {
+    let gotGcEvent = new Promise(resolve => {
       event.on(memory, "garbage-collection", gcData => {
         ok(gcData, "Got GC data");
         resolve();
diff --git a/devtools/server/tests/mochitest/test_preference.html b/devtools/server/tests/mochitest/test_preference.html
index 54903f455df8..310fd6cb4ce0 100644
--- a/devtools/server/tests/mochitest/test_preference.html
+++ b/devtools/server/tests/mochitest/test_preference.html
@@ -12,46 +12,45 @@ Bug 943251 - Allow accessing about:config from WebIDE
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 function runTests() {
-  var Cu = Components.utils;
-  var Cc = Components.classes;
-  var Ci = Components.interfaces;
+  let Cu = Components.utils;
+  let Ci = Components.interfaces;
 
-  var {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
-  var {DebuggerClient} = require("devtools/shared/client/main");
-  var {DebuggerServer} = require("devtools/server/main");
-  var Services = require("Services");
+  let {require} = Cu.import("resource://devtools/shared/Loader.jsm", {});
+  let {DebuggerClient} = require("devtools/shared/client/main");
+  let {DebuggerServer} = require("devtools/server/main");
+  let Services = require("Services");
 
   SimpleTest.waitForExplicitFinish();
 
-  var {getPreferenceFront} = require("devtools/shared/fronts/preference");
+  let {getPreferenceFront} = require("devtools/shared/fronts/preference");
 
   DebuggerServer.init();
   DebuggerServer.addBrowserActors();
 
-  var client = new DebuggerClient(DebuggerServer.connectPipe());
+  let client = new DebuggerClient(DebuggerServer.connectPipe());
   client.connect().then(function onConnect() {
-    client.listTabs(function onListTabs(aResponse) {
-      var p = getPreferenceFront(client, aResponse);
+    client.listTabs(function onListTabs(response) {
+      let p = getPreferenceFront(client, response);
 
-      var prefs = {};
+      let prefs = {};
 
-      var localPref = {
+      let localPref = {
         boolPref: true,
         intPref: 0x1234,
         charPref: "Hello World",
       };
 
-
       function checkValues() {
         is(prefs.boolPref, localPref.boolPref, "read/write bool pref");
         is(prefs.intPref, localPref.intPref, "read/write int pref");
         is(prefs.charPref, localPref.charPref, "read/write string pref");
 
-        ["test.all.bool", "test.all.int", "test.all.string"].forEach(function(key) {
-          var expectedValue;
-          switch(Services.prefs.getPrefType(key)) {
+        ["test.all.bool", "test.all.int", "test.all.string"].forEach(function (key) {
+          let expectedValue;
+          switch (Services.prefs.getPrefType(key)) {
             case Ci.nsIPrefBranch.PREF_STRING:
               expectedValue = Services.prefs.getCharPref(key);
               break;
@@ -66,37 +65,43 @@ function runTests() {
               break;
           }
 
-          is(prefs.allPrefs[key].value, expectedValue, "valid preference value (" + key + ")");
-          is(prefs.allPrefs[key].hasUserValue, Services.prefs.prefHasUserValue(key), "valid hasUserValue (" + key + ")");
+          is(prefs.allPrefs[key].value, expectedValue,
+             "valid preference value (" + key + ")");
+          is(prefs.allPrefs[key].hasUserValue, Services.prefs.prefHasUserValue(key),
+             "valid hasUserValue (" + key + ")");
         });
 
-        ["test.bool", "test.int", "test.string"].forEach(function(key) {
+        ["test.bool", "test.int", "test.string"].forEach(function (key) {
           ok(!prefs.allPrefs.hasOwnProperty(key), "expect no pref (" + key + ")");
-          is(Services.prefs.getPrefType(key), Ci.nsIPrefBranch.PREF_INVALID, "pref (" + key + ") is clear");
+          is(Services.prefs.getPrefType(key), Ci.nsIPrefBranch.PREF_INVALID,
+             "pref (" + key + ") is clear");
         });
 
         client.close().then(() => {
           DebuggerServer.destroy();
-          SimpleTest.finish()
+          SimpleTest.finish();
         });
       }
 
+      function updatePrefsProperty(key) {
+        return function (value) {
+          prefs[key] = value;
+        };
+      }
 
-      p.getAllPrefs().then((json) => prefs["allPrefs"]  = json)
+      p.getAllPrefs().then(updatePrefsProperty("allPrefs"))
       .then(() => p.setBoolPref("test.bool", localPref.boolPref))
       .then(() => p.setIntPref("test.int", localPref.intPref))
       .then(() => p.setCharPref("test.string", localPref.charPref))
-      .then(() => p.getBoolPref("test.bool")).then((value) => prefs["boolPref"] = value)
-      .then(() => p.getIntPref("test.int")).then((value) => prefs["intPref"] = value)
-      .then(() => p.getCharPref("test.string")).then((value) => prefs["charPref"] = value)
+      .then(() => p.getBoolPref("test.bool")).then(updatePrefsProperty("boolPref"))
+      .then(() => p.getIntPref("test.int")).then(updatePrefsProperty("intPref"))
+      .then(() => p.getCharPref("test.string")).then(updatePrefsProperty("charPref"))
       .then(() => p.clearUserPref("test.bool"))
       .then(() => p.clearUserPref("test.int"))
       .then(() => p.clearUserPref("test.string"))
       .then(checkValues);
-
     });
   });
-
 }
 
 window.onload = function () {
@@ -108,7 +113,7 @@ window.onload = function () {
       ["test.all.string", "allizom"],
     ]
   }, runTests);
-}
+};
 </script>
 </pre>
 </body>
diff --git a/devtools/server/tests/mochitest/test_setupInParentChild.html b/devtools/server/tests/mochitest/test_setupInParentChild.html
index 5c05e64db676..d4b1f2071152 100644
--- a/devtools/server/tests/mochitest/test_setupInParentChild.html
+++ b/devtools/server/tests/mochitest/test_setupInParentChild.html
@@ -12,6 +12,7 @@ Bug 1181100 - Test DebuggerServerConnection.setupInParent and DebuggerServer.set
 <body>
 <pre id="test">
 <script type="application/javascript">
+"use strict";
 
 let Cu = Components.utils;
 let Cc = Components.classes;
@@ -22,7 +23,7 @@ let {DebuggerClient} = require("devtools/shared/client/main");
 let {DebuggerServer} = require("devtools/server/main");
 let Services = require("Services");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
   SpecialPowers.pushPrefEnv({
@@ -32,7 +33,7 @@ window.onload = function() {
       ["dom.mozBrowserFramesEnabled", true]
     ]
   }, runTests);
-}
+};
 
 function runTests() {
   // Create a minimal iframe with a message manager
@@ -40,8 +41,6 @@ function runTests() {
   iframe.mozbrowser = true;
   document.body.appendChild(iframe);
 
-  let mm = iframe.frameLoader.messageManager;
-
   // Instantiate a minimal server
   if (!DebuggerServer.initialized) {
     DebuggerServer.init();
@@ -76,7 +75,7 @@ function runTests() {
 
   // Wait also for a reponse from setupInParent called from setup-in-child.js
   let onParent = (_, topic, args) => {
-    Services.obs.removeObserver(onParent, "test:setupParent", false);
+    Services.obs.removeObserver(onParent, "test:setupParent");
     args = JSON.parse(args);
 
     is(args[0], true, "Got `mm` argument, a message manager");
@@ -99,10 +98,9 @@ function runTests() {
     client.close().then(function () {
       DebuggerServer.destroy();
       iframe.remove();
-      SimpleTest.finish()
+      SimpleTest.finish();
     });
   }
-
 }
 </script>
 </pre>
diff --git a/devtools/server/tests/mochitest/test_styles-applied.html b/devtools/server/tests/mochitest/test_styles-applied.html
index be446c69908a..3fd8c9eb10a8 100644
--- a/devtools/server/tests/mochitest/test_styles-applied.html
+++ b/devtools/server/tests/mochitest/test_styles-applied.html
@@ -11,25 +11,23 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/server/actors/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gStyles = null;
-var gClient = null;
+let gWalker = null;
+let gStyles = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
       return inspector.getPageStyle();
     }).then(styles => {
@@ -50,23 +48,28 @@ addTest(function inheritedUserStyles() {
     is(applied[1].inherited.id, "uninheritable-rule-inheritable-style",
        "Entry 1 should be inherited from the parent");
     is(applied[1].rule.type, 100, "Entry 1 should be an element style");
-    is(applied[1].rule.cssText, "color: red;", "Entry 1 should have the expected cssText");
+    is(applied[1].rule.cssText, "color: red;",
+       "Entry 1 should have the expected cssText");
 
     is(applied[2].inherited.id, "inheritable-rule-inheritable-style",
        "Entry 2 should be inherited from the parent's parent");
     is(applied[2].rule.type, 100, "Entry 2 should be an element style");
-    is(applied[2].rule.cssText, "color: blue;", "Entry 2 should have the expected cssText");
+    is(applied[2].rule.cssText, "color: blue;",
+       "Entry 2 should have the expected cssText");
 
     is(applied[3].inherited.id, "inheritable-rule-inheritable-style",
        "Entry 3 should be inherited from the parent's parent");
     is(applied[3].rule.type, 1, "Entry 3 should be a rule style");
-    is(applied[3].rule.cssText, "font-size: 15px;", "Entry 3 should have the expected cssText");
-    ok(!applied[3].matchedSelectors, "Shouldn't get matchedSelectors with this request.");
+    is(applied[3].rule.cssText, "font-size: 15px;",
+       "Entry 3 should have the expected cssText");
+    ok(!applied[3].matchedSelectors,
+       "Shouldn't get matchedSelectors with this request.");
 
     is(applied[4].inherited.id, "inheritable-rule-uninheritable-style",
        "Entry 4 should be inherited from the parent's parent");
     is(applied[4].rule.type, 1, "Entry 4 should be an rule style");
-    is(applied[4].rule.cssText, "font-size: 15px;", "Entry 4 should have the expected cssText");
+    is(applied[4].rule.cssText, "font-size: 15px;",
+       "Entry 4 should have the expected cssText");
     ok(!applied[4].matchedSelectors, "Shouldn't get matchedSelectors with this request.");
 
     is(applied.length, 5, "Should have 5 rules.");
@@ -106,8 +109,10 @@ addTest(function matchedSelectors() {
       inherited: true, filter: "user", matchedSelectors: true
     });
   }).then(applied => {
-    is(applied[3].matchedSelectors[0], ".inheritable-rule", "Entry 3 should have a matched selector");
-    is(applied[4].matchedSelectors[0], ".inheritable-rule", "Entry 4 should have a matched selector");
+    is(applied[3].matchedSelectors[0], ".inheritable-rule",
+       "Entry 3 should have a matched selector");
+    is(applied[4].matchedSelectors[0], ".inheritable-rule",
+       "Entry 4 should have a matched selector");
   }).then(runNextTest));
 });
 
@@ -124,9 +129,8 @@ addTest(function testMediaQuery() {
 });
 
 addTest(function cleanup() {
-  delete gStyles;
-  delete gWalker;
-  delete gClient;
+  gStyles = null;
+  gWalker = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_styles-computed.html b/devtools/server/tests/mochitest/test_styles-computed.html
index 8fd6d8d25db7..f7fd28fddd19 100644
--- a/devtools/server/tests/mochitest/test_styles-computed.html
+++ b/devtools/server/tests/mochitest/test_styles-computed.html
@@ -11,26 +11,23 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/server/actors/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gStyles = null;
-var gClient = null;
+let gWalker = null;
+let gStyles = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
-    gInspectee = doc;
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
       return inspector.getPageStyle();
     }).then(styles => {
@@ -40,87 +37,87 @@ addTest(function setup() {
 });
 
 addTest(function testComputed() {
-  let localNode = gInspectee.querySelector("#computed-test-node");
-  let elementStyle = null;
-  promiseDone(gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
-    return gStyles.getComputed(node, {});
-  }).then(computed => {
-    // Test a smattering of properties that include some system-defined
-    // props, some props that were defined in this node's stylesheet,
-    // and some default props.
-    is(computed["white-space"].value, "normal", "Default value should appear");
-    is(computed["display"].value, "block", "System stylesheet item should appear");
-    is(computed["cursor"].value, "crosshair", "Included stylesheet rule should appear");
-    is(computed["color"].value, "rgb(255, 0, 0)", "Inherited style attribute should appear");
-    is(computed["font-size"].value, "15px", "Inherited inline rule should appear");
+  promiseDone(
+    gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
+      return gStyles.getComputed(node, {});
+    }).then(computed => {
+      // Test a smattering of properties that include some system-defined
+      // props, some props that were defined in this node's stylesheet,
+      // and some default props.
+      is(computed["white-space"].value, "normal", "Default value should appear");
+      is(computed.display.value, "block", "System stylesheet item should appear");
+      is(computed.cursor.value, "crosshair", "Included stylesheet rule should appear");
+      is(computed.color.value, "rgb(255, 0, 0)",
+         "Inherited style attribute should appear");
+      is(computed["font-size"].value, "15px", "Inherited inline rule should appear");
 
-    // We didn't request markMatched, so these shouldn't be set
-    ok(!computed["cursor"].matched, "Didn't ask for matched, shouldn't get it");
-    ok(!computed["color"].matched, "Didn't ask for matched, shouldn't get it");
-    ok(!computed["font-size"].matched, "Didn't ask for matched, shouldn't get it");
-  }).then(runNextTest));
+      // We didn't request markMatched, so these shouldn't be set
+      ok(!computed.cursor.matched, "Didn't ask for matched, shouldn't get it");
+      ok(!computed.color.matched, "Didn't ask for matched, shouldn't get it");
+      ok(!computed["font-size"].matched, "Didn't ask for matched, shouldn't get it");
+    }).then(runNextTest)
+  );
 });
 
 addTest(function testComputedUserMatched() {
-  let localNode = gInspectee.querySelector("#computed-test-node");
-  let elementStyle = null;
-  promiseDone(gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
-    return gStyles.getComputed(node, { filter: "user", markMatched: true });
-  }).then(computed => {
-    ok(!computed["white-space"].matched, "Default style shouldn't match");
-    ok(!computed["display"].matched, "Only user styles should match");
-    ok(computed["cursor"].matched, "Asked for matched, should get it");
-    ok(computed["color"].matched, "Asked for matched, should get it");
-    ok(computed["font-size"].matched, "Asked for matched, should get it");
-  }).then(runNextTest));
+  promiseDone(
+    gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
+      return gStyles.getComputed(node, { filter: "user", markMatched: true });
+    }).then(computed => {
+      ok(!computed["white-space"].matched, "Default style shouldn't match");
+      ok(!computed.display.matched, "Only user styles should match");
+      ok(computed.cursor.matched, "Asked for matched, should get it");
+      ok(computed.color.matched, "Asked for matched, should get it");
+      ok(computed["font-size"].matched, "Asked for matched, should get it");
+    }).then(runNextTest)
+  );
 });
 
 addTest(function testComputedSystemMatched() {
-  let localNode = gInspectee.querySelector("#computed-test-node");
-  let elementStyle = null;
-  promiseDone(gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
-    return gStyles.getComputed(node, { filter: "ua", markMatched: true });
-  }).then(computed => {
-    ok(!computed["white-space"].matched, "Default style shouldn't match");
-    ok(computed["display"].matched, "System stylesheets should match");
-    ok(computed["cursor"].matched, "Asked for matched, should get it");
-    ok(computed["color"].matched, "Asked for matched, should get it");
-    ok(computed["font-size"].matched, "Asked for matched, should get it");
-  }).then(runNextTest));
+  promiseDone(
+    gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
+      return gStyles.getComputed(node, { filter: "ua", markMatched: true });
+    }).then(computed => {
+      ok(!computed["white-space"].matched, "Default style shouldn't match");
+      ok(computed.display.matched, "System stylesheets should match");
+      ok(computed.cursor.matched, "Asked for matched, should get it");
+      ok(computed.color.matched, "Asked for matched, should get it");
+      ok(computed["font-size"].matched, "Asked for matched, should get it");
+    }).then(runNextTest)
+  );
 });
 
 addTest(function testComputedUserOnlyMatched() {
-  let localNode = gInspectee.querySelector("#computed-test-node");
-  let elementStyle = null;
-  promiseDone(gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
-    return gStyles.getComputed(node, { filter: "user", onlyMatched: true });
-  }).then(computed => {
-    ok(!("white-space" in computed), "Default style shouldn't exist");
-    ok(!("display" in computed), "System stylesheets shouldn't exist");
-    ok(("cursor" in computed), "User items should exist.");
-    ok(("color" in computed), "User items should exist.");
-    ok(("font-size" in computed), "User items should exist.");
-  }).then(runNextTest));
+  promiseDone(
+    gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
+      return gStyles.getComputed(node, { filter: "user", onlyMatched: true });
+    }).then(computed => {
+      ok(!("white-space" in computed), "Default style shouldn't exist");
+      ok(!("display" in computed), "System stylesheets shouldn't exist");
+      ok(("cursor" in computed), "User items should exist.");
+      ok(("color" in computed), "User items should exist.");
+      ok(("font-size" in computed), "User items should exist.");
+    }).then(runNextTest)
+  );
 });
 
 addTest(function testComputedSystemOnlyMatched() {
-  let localNode = gInspectee.querySelector("#computed-test-node");
-  let elementStyle = null;
-  promiseDone(gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
-    return gStyles.getComputed(node, { filter: "ua", onlyMatched: true });
-  }).then(computed => {
-    ok(!("white-space" in computed), "Default style shouldn't exist");
-    ok(("display" in computed), "System stylesheets should exist");
-    ok(("cursor" in computed), "User items should exist.");
-    ok(("color" in computed), "User items should exist.");
-    ok(("font-size" in computed), "User items should exist.");
-  }).then(runNextTest));
+  promiseDone(
+    gWalker.querySelector(gWalker.rootNode, "#computed-test-node").then(node => {
+      return gStyles.getComputed(node, { filter: "ua", onlyMatched: true });
+    }).then(computed => {
+      ok(!("white-space" in computed), "Default style shouldn't exist");
+      ok(("display" in computed), "System stylesheets should exist");
+      ok(("cursor" in computed), "User items should exist.");
+      ok(("color" in computed), "User items should exist.");
+      ok(("font-size" in computed), "User items should exist.");
+    }).then(runNextTest)
+  );
 });
 
 addTest(function cleanup() {
-  delete gStyles;
-  delete gWalker;
-  delete gClient;
+  gStyles = null;
+  gWalker = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_styles-layout.html b/devtools/server/tests/mochitest/test_styles-layout.html
index cac8c670c46e..e9f11d5511bb 100644
--- a/devtools/server/tests/mochitest/test_styles-layout.html
+++ b/devtools/server/tests/mochitest/test_styles-layout.html
@@ -9,7 +9,7 @@
 <script type="application/javascript">
 "use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
 };
@@ -17,9 +17,9 @@ window.onload = function() {
 let gWalker = null;
 let gStyles = null;
 
-addTest(function() {
+addTest(function () {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
@@ -32,12 +32,12 @@ addTest(function() {
   });
 });
 
-addTest(function() {
+addTest(function () {
   ok(gStyles.getLayout, "The PageStyleActor has a getLayout method");
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   let node = yield gWalker.querySelector(gWalker.rootNode, "#layout-element");
   let layout = yield gStyles.getLayout(node, {});
 
@@ -55,7 +55,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   let node = yield gWalker.querySelector(gWalker.rootNode, "#layout-element");
   let layout = yield gStyles.getLayout(node, {});
 
@@ -79,7 +79,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addAsyncTest(function*() {
+addAsyncTest(function* () {
   let node = yield gWalker.querySelector(gWalker.rootNode,
                                          "#layout-auto-margin-element");
 
@@ -98,7 +98,7 @@ addAsyncTest(function*() {
   runNextTest();
 });
 
-addTest(function() {
+addTest(function () {
   gStyles = gWalker = null;
   runNextTest();
 });
diff --git a/devtools/server/tests/mochitest/test_styles-matched.html b/devtools/server/tests/mochitest/test_styles-matched.html
index dfe2d3207468..bbfd8cafd6b8 100644
--- a/devtools/server/tests/mochitest/test_styles-matched.html
+++ b/devtools/server/tests/mochitest/test_styles-matched.html
@@ -11,27 +11,27 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/server/actors/inspector");
+"use strict";
+
 const CssLogic = require("devtools/shared/inspector/css-logic");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gStyles = null;
-var gClient = null;
+let gWalker = null;
+let gStyles = null;
+let gInspectee = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     gInspectee = doc;
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
       return inspector.getPageStyle();
     }).then(styles => {
@@ -47,17 +47,22 @@ addTest(function testMatchedStyles() {
     is(matched[0].sourceText, "this.style", "First match comes from the element style");
     is(matched[0].selector, "@element.style", "Element style has a special selector");
     is(matched[0].value, "10px", "First match has the expected value");
-    is(matched[0].status, CssLogic.STATUS.BEST, "First match is the best match")
+    is(matched[0].status, CssLogic.STATUS.BEST, "First match is the best match");
     is(matched[0].rule.type, 100, "First match is an element style");
-    is(matched[0].rule.href, gInspectee.defaultView.location.href, "Node style comes from this document")
+    is(matched[0].rule.href, gInspectee.defaultView.location.href,
+       "Node style comes from this document");
 
     is(matched[1].sourceText, ".inheritable-rule", "Second match comes from a rule");
     is(matched[1].selector, ".inheritable-rule", "Second style has a selector");
     is(matched[1].value, "15px", "Second match has the expected value");
-    is(matched[1].status, CssLogic.STATUS.PARENT_MATCH, "Second match is from the parent")
-    is(matched[1].rule.parentStyleSheet.href, null, "Inline stylesheet shouldn't have an href");
-    is(matched[1].rule.parentStyleSheet.nodeHref, gInspectee.defaultView.location.href, "Inline stylesheet's nodeHref should match the current document");
-    ok(!matched[1].rule.parentStyleSheet.system, "Inline stylesheet shouldn't be a system stylesheet.");
+    is(matched[1].status, CssLogic.STATUS.PARENT_MATCH,
+       "Second match is from the parent");
+    is(matched[1].rule.parentStyleSheet.href, null,
+       "Inline stylesheet shouldn't have an href");
+    is(matched[1].rule.parentStyleSheet.nodeHref, gInspectee.defaultView.location.href,
+       "Inline stylesheet's nodeHref should match the current document");
+    ok(!matched[1].rule.parentStyleSheet.system,
+       "Inline stylesheet shouldn't be a system stylesheet.");
   }).then(runNextTest));
 });
 
@@ -77,9 +82,9 @@ addTest(function testSystemStyles() {
 });
 
 addTest(function cleanup() {
-  delete gStyles;
-  delete gWalker;
-  delete gClient;
+  gStyles = null;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_styles-modify.html b/devtools/server/tests/mochitest/test_styles-modify.html
index ea453197d988..5e9c558c0afd 100644
--- a/devtools/server/tests/mochitest/test_styles-modify.html
+++ b/devtools/server/tests/mochitest/test_styles-modify.html
@@ -11,26 +11,26 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/server/actors/inspector");
+"use strict";
+
 const {isCssPropertyKnown} = require("devtools/server/actors/css-properties");
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
 var gWalker = null;
 var gStyles = null;
-var gClient = null;
+var gInspectee = null;
 
 addAsyncTest(function* setup() {
   let url = document.getElementById("inspectorContent").href;
   let inspector;
 
   yield new Promise(resolve => {
-    attachURL(url, function(err, client, tab, doc) {
+    attachURL(url, function (err, client, tab, doc) {
       gInspectee = doc;
-      gClient = client;
       let {InspectorFront} = require("devtools/shared/fronts/inspector");
       inspector = InspectorFront(client, tab);
       resolve();
@@ -95,9 +95,9 @@ function* removeProperty(rule, index, name) {
 }
 
 addTest(function cleanup() {
-  delete gStyles;
-  delete gWalker;
-  delete gClient;
+  gStyles = null;
+  gWalker = null;
+  gInspectee = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_styles-svg.html b/devtools/server/tests/mochitest/test_styles-svg.html
index 21ca161c98ca..37dafe4d37e4 100644
--- a/devtools/server/tests/mochitest/test_styles-svg.html
+++ b/devtools/server/tests/mochitest/test_styles-svg.html
@@ -12,25 +12,23 @@ Bug 921191 - allow inspection/editing of SVG elements' CSS properties
   <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="application/javascript" src="inspector-helpers.js"></script>
   <script type="application/javascript">
-const inspector = require("devtools/server/actors/inspector");
+"use strict";
 
-window.onload = function() {
+window.onload = function () {
   SimpleTest.waitForExplicitFinish();
   runNextTest();
-}
+};
 
-var gWalker = null;
-var gStyles = null;
-var gClient = null;
+let gWalker = null;
+let gStyles = null;
 
 addTest(function setup() {
   let url = document.getElementById("inspectorContent").href;
-  attachURL(url, function(err, client, tab, doc) {
+  attachURL(url, function (err, client, tab, doc) {
     let {InspectorFront} = require("devtools/shared/fronts/inspector");
     let inspector = InspectorFront(client, tab);
     promiseDone(inspector.getWalker().then(walker => {
       ok(walker, "getWalker() should return an actor.");
-      gClient = client;
       gWalker = walker;
       return inspector.getPageStyle();
     }).then(styles => {
@@ -49,9 +47,8 @@ addTest(function inheritedUserStyles() {
 });
 
 addTest(function cleanup() {
-  delete gStyles;
-  delete gWalker;
-  delete gClient;
+  gStyles = null;
+  gWalker = null;
   runNextTest();
 });
 
diff --git a/devtools/server/tests/mochitest/test_unsafeDereference.html b/devtools/server/tests/mochitest/test_unsafeDereference.html
index df44fac516c9..2877358b2db8 100644
--- a/devtools/server/tests/mochitest/test_unsafeDereference.html
+++ b/devtools/server/tests/mochitest/test_unsafeDereference.html
@@ -16,6 +16,7 @@ xray wrapper.
 <body>
 <pre id="test">
 <script>
+"use strict";
 
 Components.utils.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
@@ -23,28 +24,28 @@ addDebuggerToGlobal(this);
 window.onload = function () {
   SimpleTest.waitForExplicitFinish();
 
-  var iframe = document.createElement("iframe");
+  let iframe = document.createElement("iframe");
   iframe.src = "http://mochi.test:8888/chrome/devtools/server/tests/mochitest/nonchrome_unsafeDereference.html";
 
   iframe.onload = function () {
-    var dbg = new Debugger;
-    var contentDO = dbg.addDebuggee(iframe.contentWindow);
-    var xhrDesc = contentDO.getOwnPropertyDescriptor('xhr');
+    let dbg = new Debugger();
+    let contentDO = dbg.addDebuggee(iframe.contentWindow);
+    let xhrDesc = contentDO.getOwnPropertyDescriptor("xhr");
 
     isnot(xhrDesc, undefined, "xhr should be visible as property of content global");
     isnot(xhrDesc.value, undefined, "xhr should have a value");
 
-    var xhr = xhrDesc.value.unsafeDereference();
+    let xhr = xhrDesc.value.unsafeDereference();
 
     is(typeof xhr, "object", "we should be able to deference xhr's value's D.O");
     is(xhr.timeout, 1742, "chrome should see the xhr's 'timeout' property");
     is(xhr.expando, undefined, "chrome should not see the xhr's 'expando' property");
 
     SimpleTest.finish();
-  }
+  };
 
   document.body.appendChild(iframe);
-}
+};
 
 </script>
 </pre>
diff --git a/devtools/server/tests/mochitest/test_websocket-server.html b/devtools/server/tests/mochitest/test_websocket-server.html
index 583d96dd9ef1..f6b97d76d3f6 100644
--- a/devtools/server/tests/mochitest/test_websocket-server.html
+++ b/devtools/server/tests/mochitest/test_websocket-server.html
@@ -9,7 +9,9 @@
 </head>
 <body>
 <script>
-window.onload = function() {
+"use strict";
+
+window.onload = function () {
   const { Constructor: CC, utils: Cu } = Components;
   const { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
   const { Task } = require("devtools/shared/task");
@@ -76,7 +78,7 @@ window.onload = function() {
     client.close();
     yield closed;
   });
-}
+};
 </script>
 </body>
 </html>