diff --git a/browser/modules/BrowserWindowTracker.sys.mjs b/browser/modules/BrowserWindowTracker.sys.mjs
index 0cd9e9630fff20d71dc1dd7367ae6af4f7a53f71..7212c5f4745f3c93c1ede932af1b0e85580aa679 100644
--- a/browser/modules/BrowserWindowTracker.sys.mjs
+++ b/browser/modules/BrowserWindowTracker.sys.mjs
@@ -326,6 +326,7 @@ export const BrowserWindowTracker = {
     args = null,
     remote = undefined,
     fission = undefined,
+    zenSyncedWindow = true,
   } = {}) {
     let windowFeatures = "chrome,dialog=no";
     if (all) {
@@ -382,6 +383,12 @@ export const BrowserWindowTracker = {
       windowFeatures,
       args
     );
+    win._zenStartupSyncFlag = Services.prefs.getBoolPref("zen.window-sync.prefer-unsynced-windows")
+      ? (zenSyncedWindow ? 'unsynced' : 'synced')
+      : (zenSyncedWindow ? 'synced' : 'unsynced');
+    if (win._zenStartupSyncFlag === 'unsynced' && openerWindow) {
+      win._zenStartupUnsyncedUserContextId = openerWindow.gZenWorkspaces.getCurrentSpaceContainerId();
+    }
     this.registerOpeningWindow(win, isPrivate);
 
     win.addEventListener(