--- a/embedding/components/windowwatcher/src/nsWindowWatcher.cpp
+++ b/embedding/components/windowwatcher/src/nsWindowWatcher.cpp
@@ -56,16 +56,20 @@
 #include "nsIPresShell.h"
 #include "nsPresContext.h"
 #include "nsContentUtils.h"
 #include "nsIPrefBranch.h"
 #include "nsIPrefService.h"
 #include "nsSandboxFlags.h"
 #include "mozilla/Preferences.h"
 
+#ifndef MOZ_PER_WINDOW_PRIVATE_BROWSING
+#include "nsIPrivateBrowsingService.h"
+#endif
+
 #ifdef USEWEAKREFS
 #include "nsIWeakReference.h"
 #endif
 
 using namespace mozilla;
 
 static const char *sJSStackContractID="@mozilla.org/js/xpc/ContextStack;1";
 
@@ -899,16 +903,27 @@ nsWindowWatcher::OpenWindowInternal(nsID
   }
 
   if (windowIsNew) {
     // See if the caller has requested a private browsing window, or if all
     // windows should be private.
     bool isPrivateBrowsingWindow =
       Preferences::GetBool("browser.privatebrowsing.autostart") ||
       !!(chromeFlags & nsIWebBrowserChrome::CHROME_PRIVATE_WINDOW);
+
+#ifndef MOZ_PER_WINDOW_PRIVATE_BROWSING
+    nsCOMPtr<nsIPrivateBrowsingService> pbs =
+      do_GetService(NS_PRIVATE_BROWSING_SERVICE_CONTRACTID);
+    if (pbs) {
+      bool inPrivateBrowsing = false;
+      pbs->GetPrivateBrowsingEnabled(&inPrivateBrowsing);
+      isPrivateBrowsingWindow |= inPrivateBrowsing;
+    }
+#endif
+
     // Otherwise, propagate the privacy status of the parent window, if
     // available, to the child.
     if (!isPrivateBrowsingWindow) {
       nsCOMPtr<nsIDocShellTreeItem> parentItem;
       GetWindowTreeItem(aParent, getter_AddRefs(parentItem));
       nsCOMPtr<nsILoadContext> parentContext = do_QueryInterface(parentItem);
       if (parentContext) {
         isPrivateBrowsingWindow = parentContext->UsePrivateBrowsing();