diff --git a/mozilla/xpfe/bootstrap/nsNativeAppSupportOS2.cpp b/mozilla/xpfe/bootstrap/nsNativeAppSupportOS2.cpp
index 2f7222e2ce8..f9357dfcf5f 100644
--- a/mozilla/xpfe/bootstrap/nsNativeAppSupportOS2.cpp
+++ b/mozilla/xpfe/bootstrap/nsNativeAppSupportOS2.cpp
@@ -2296,6 +2296,16 @@ nsNativeAppSupportOS2::StartServerMode() {
         // We dont have to anything anymore. The native UI
         // will create the window
         return NS_OK;
+    } else {
+        // Sometimes a window will have been opened even though mShouldShowUI is false
+        // (e.g., mozilla -mail -turbo).  Detect that by testing whether there's a
+        // window already open.
+        nsCOMPtr<nsIDOMWindowInternal> win;
+        GetMostRecentWindow( 0, getter_AddRefs( win ) );
+        if ( win ) {
+            // Window already opened, don't need this special Nav window.
+            return NS_OK;
+        }
     }
 
     // Since native UI wont create any window, we create a hidden window