Bug 1901840 - restore browser.privateWindowSeparation.enabled pref r=nshukla,firefox-desktop-core-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D213651

browser/app/profile/firefox.js

@@ -822,6 +822,10 @@ pref("browser.dataFeatureRecommendations.enabled", false);
 // sets darkTheme data.
 pref("browser.theme.dark-private-windows", true);
 
+// Pref to control whether or not Private Browsing windows show up
+// as separate icons in the Windows taskbar.
+pref("browser.privateWindowSeparation.enabled", true);
+
 // Controls visibility of the privacy segmentation preferences section.
 pref("browser.privacySegmentation.preferences.show", false);
 

browser/components/BrowserContentHandler.sys.mjs

@@ -322,7 +322,13 @@ function openBrowserWindow(
           Ci.nsILoadContext
         ).usePrivateBrowsing = true;
 
-        if (AppConstants.platform == "win") {
+        if (
+          AppConstants.platform == "win" &&
+          Services.prefs.getBoolPref(
+            "browser.privateWindowSeparation.enabled",
+            true
+          )
+        ) {
           lazy.WinTaskbar.setGroupIdForWindow(
             win,
             lazy.WinTaskbar.defaultPrivateGroupId

browser/components/BrowserGlue.sys.mjs

@@ -2756,6 +2756,10 @@ BrowserGlue.prototype = {
         name: "ensurePrivateBrowsingShortcutExists",
         condition:
           AppConstants.platform == "win" &&
+          Services.prefs.getBoolPref(
+            "browser.privateWindowSeparation.enabled",
+            true
+          ) &&
           // We don't want a shortcut if it's been disabled, eg: by enterprise policy.
           lazy.PrivateBrowsingUtils.enabled &&
           // Private Browsing shortcuts for packaged builds come with the package,

widget/windows/nsWindow.cpp

@@ -993,7 +993,8 @@ nsresult nsWindow::Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
     }
   }
 
-  if (aInitData->mIsPrivate) {
+  if (Preferences::GetBool("browser.privateWindowSeparation.enabled", true) &&
+      (aInitData->mIsPrivate)) {
     // 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