Bug 1782295: Use Nimbus for Felt Privacy window separation r=dao

We'll be defaulting Felt Privacy features to enabled, and allowing them to be disabled by Nimbus (primarily for a holdback study).

Differential Revision: https://phabricator.services.mozilla.com/D153275

browser/app/profile/firefox.js

@@ -654,9 +654,8 @@ pref("browser.privatebrowsing.enable-new-logo", true);
 pref("browser.privacySegmentation.enabled", false);
 
 // Temporary pref to control whether or not Private Browsing windows show up
-// as separate icons in the Windows taskbar. This will be removed and become
-// the default behaviour with 106.
-pref("browser.privacySegmentation.windowSeparation.enabled", false);
+// as separate icons in the Windows taskbar.
+pref("browser.privacySegmentation.windowSeparation.enabled", true);
 
 // Use dark theme variant for PBM windows. This is only supported if the theme
 // sets darkTheme data.

browser/components/BrowserContentHandler.jsm

@@ -22,6 +22,7 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   HomePage: "resource:///modules/HomePage.jsm",
   FirstStartup: "resource://gre/modules/FirstStartup.jsm",
   LaterRun: "resource:///modules/LaterRun.jsm",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.jsm",
   SessionStartup: "resource:///modules/sessionstore/SessionStartup.jsm",
   ShellService: "resource:///modules/ShellService.jsm",
@@ -44,8 +45,6 @@ const ONCE_PREF = "browser.startup.homepage_override.once";
 // Index of Private Browsing icon in firefox.exe
 // Must line up with the one in nsNativeAppSupportWin.h.
 const PRIVATE_BROWSING_ICON_INDEX = 5;
-const PRIVATE_WINDOW_SEPARATION_PREF =
-  "browser.privacySegmentation.windowSeparation.enabled";
 
 function shouldLoadURI(aURI) {
   if (aURI && !aURI.schemeIs("chrome")) {
@@ -283,11 +282,11 @@ function openBrowserWindow(
         win.docShell.QueryInterface(
           Ci.nsILoadContext
         ).usePrivateBrowsing = true;
-        if (Services.prefs.getBoolPref(PRIVATE_WINDOW_SEPARATION_PREF)) {
-          // TODO: Changing this after the Window has been painted causes it to
-          // change Taskbar icons if the original one had a different AUMID.
-          // This must stay pref'ed off until this is resolved.
-          // https://bugzilla.mozilla.org/show_bug.cgi?id=1751010
+        if (
+          lazy.NimbusFeatures.majorRelease2022.getVariable(
+            "feltPrivacyWindowSeparation"
+          )
+        ) {
           lazy.WinTaskbar.setGroupIdForWindow(
             win,
             lazy.WinTaskbar.defaultPrivateGroupId

browser/components/BrowserGlue.jsm

@@ -143,8 +143,6 @@ const PRIVATE_BROWSING_BINARY = "private_browsing.exe";
 // Index of Private Browsing icon in private_browsing.exe
 // Must line up with IDI_PBICON_PB_PB_EXE in nsNativeAppSupportWin.h.
 const PRIVATE_BROWSING_EXE_ICON_INDEX = 1;
-const PREF_PRIVATE_WINDOW_SEPARATION =
-  "browser.privacySegmentation.windowSeparation.enabled";
 const PREF_PRIVATE_BROWSING_SHORTCUT_CREATED =
   "browser.privacySegmentation.createdShortcut";
 
@@ -2536,7 +2534,9 @@ BrowserGlue.prototype = {
           // Pref'ed off until Private Browsing window separation is enabled by default
           // to avoid a situation where a user pins the Private Browsing shortcut to
           // the Taskbar, which will end up launching into a different Taskbar icon.
-          Services.prefs.getBoolPref(PREF_PRIVATE_WINDOW_SEPARATION, false) &&
+          lazy.NimbusFeatures.majorRelease2022.getVariable(
+            "feltPrivacyWindowSeparation"
+          ) &&
           // Private Browsing shortcuts for packaged builds come with the package,
           // if they exist at all. We shouldn't try to create our own.
           !Services.sysinfo.getProperty("hasWinPackageId") &&

toolkit/components/nimbus/FeatureManifest.yaml

@@ -602,3 +602,7 @@ majorRelease2022:
       type: boolean
       fallbackPref: "browser.privacySegmentation.preferences.show"
       description: "Controls visibility of the privacy segmentation preferences section."
+    feltPrivacyWindowSeparation:
+      type: boolean
+      fallbackPref: "browser.privacySegmentation.windowSeparation.enabled"
+      description: "Whether or not private browsing windows use a separate icon in the Windows taskbar"

widget/windows/nsWindow.cpp

@@ -160,6 +160,7 @@
 #include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/StaticPrefs_widget.h"
 #include "nsNativeAppSupportWin.h"
+#include "mozilla/browser/NimbusFeatures.h"
 
 #include "nsIGfxInfo.h"
 #include "nsUXThemeConstants.h"
@@ -1112,8 +1113,8 @@ nsresult nsWindow::Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
   }
 
   if (aInitData->mIsPrivate) {
-    if (Preferences::GetBool(
-            "browser.privacySegmentation.windowSeparation.enabled", false) &&
+    if (NimbusFeatures::GetBool("majorRelease2022"_ns,
+                                "feltPrivacyWindowSeparation"_ns, true) &&
         // Although permanent Private Browsing mode is indeed Private Browsing,
         // we choose to make it look like regular Firefox in terms of the icon
         // it uses (which also means we shouldn't use the Private Browsing