fixup! Bug 40926: Implemented the New Identity feature

Move to HTML stylesheets instead of XML ones to be coherent with
upstream.

Also, switch from XPCOMUtils to ChromeUtils.

browser/components/newidentity/content/newIdentityDialog.xhtml

@@ -6,11 +6,6 @@
 
 <!-- based on resetProfile.xhtml -->
 
-<?xml-stylesheet href="chrome://global/skin/global.css"?>
-<?xml-stylesheet href="chrome://global/content/commonDialog.css"?>
-<?xml-stylesheet href="chrome://global/skin/commonDialog.css"?>
-<?xml-stylesheet href="chrome://browser/content/newIdentityDialog.css"?>
-
 <window
   id="newIdentityDialogWindow"
   xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
@@ -21,6 +16,20 @@
 >
   <dialog id="newIdentityDialog" buttons="accept,cancel" defaultButton="accept">
     <linkset>
+      <html:link rel="stylesheet" href="chrome://global/skin/global.css" />
+      <html:link
+        rel="stylesheet"
+        href="chrome://global/content/commonDialog.css"
+      />
+      <html:link
+        rel="stylesheet"
+        href="chrome://global/skin/commonDialog.css"
+      />
+      <html:link
+        rel="stylesheet"
+        href="chrome://browser/content/newIdentityDialog.css"
+      />
+
       <html:link rel="localization" href="branding/brand.ftl" />
       <html:link rel="localization" href="toolkit/global/base-browser.ftl" />
     </linkset>

browser/components/newidentity/content/newidentity.js

@@ -4,7 +4,7 @@
 
 // Use a lazy getter because NewIdentityButton is declared more than once
 // otherwise.
-XPCOMUtils.defineLazyGetter(this, "NewIdentityButton", () => {
+ChromeUtils.defineLazyGetter(this, "NewIdentityButton", () => {
   // Logger adapted from CustomizableUI.jsm
   const logger = (() => {
     const { ConsoleAPI } = ChromeUtils.import(
@@ -314,11 +314,10 @@ XPCOMUtils.defineLazyGetter(this, "NewIdentityButton", () => {
 
     clearPreferencesAndPermissions() {
       logger.info("Clearing Content Preferences");
-      ChromeUtils.defineModuleGetter(
-        this,
-        "PrivateBrowsingUtils",
-        "resource://gre/modules/PrivateBrowsingUtils.jsm"
-      );
+      ChromeUtils.defineESModuleGetters(this, {
+        PrivateBrowsingUtils:
+          "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
+      });
       const pbCtxt = PrivateBrowsingUtils.privacyContextFromWindow(window);
       const cps = Cc["@mozilla.org/content-pref/service;1"].getService(
         Ci.nsIContentPrefService2