diff --git a/mailnews/compose/src/nsMsgComposeService.cpp b/mailnews/compose/src/nsMsgComposeService.cpp
index 67d84454ea76..835c550a2d54 100644
--- a/mailnews/compose/src/nsMsgComposeService.cpp
+++ b/mailnews/compose/src/nsMsgComposeService.cpp
@@ -77,6 +77,7 @@
 #include "nsMsgBaseCID.h"
 #include "nsIMsgAccountManager.h"
 #include "nsIMimeMiscStatus.h"
+#include "nsXPFEComponentsCID.h"
 
 #include "nsIInterfaceRequestorUtils.h"
 
@@ -95,6 +96,7 @@
 
 #ifdef MOZ_XUL_APP
 #include "nsICommandLine.h"
+#include "nsIAppStartup.h"
 #endif
 
 #ifdef XP_WIN32
@@ -234,7 +236,7 @@ void nsMsgComposeService::DeleteCachedWindows()
   PRInt32 i;
   for (i = 0; i < mMaxRecycledWindows; i ++)
   {
-    CloseWindow(mCachedWindows[i].window);
+    CloseHiddenCachedWindow(mCachedWindows[i].window);
     mCachedWindows[i].Clear();
   }
 }
@@ -305,7 +307,7 @@ nsresult nsMsgComposeService::OpenWindow(const char *chrome, nsIMsgComposeParams
   return rv;
 }
 
-void nsMsgComposeService::CloseWindow(nsIDOMWindowInternal *domWindow)
+void nsMsgComposeService::CloseHiddenCachedWindow(nsIDOMWindowInternal *domWindow)
 {
   if (domWindow)
   {
@@ -324,8 +326,20 @@ void nsMsgComposeService::CloseWindow(nsIDOMWindowInternal *domWindow)
         {
           nsCOMPtr<nsIBaseWindow> baseWindow;
           baseWindow = do_QueryInterface(treeOwner);
-          if (baseWindow)
+          if (baseWindow) {
+#ifdef MOZ_XUL_APP
+            // HACK ALERT: when we hid this window we fired the "xul-window-destroyed"
+            // notification for it. Now that it's being really-destroyed it will fire that
+            // notification *again* for itself. The appstartup code maintains an internal
+            // reference count of windows that block app shutdown: we want to increment that
+            // count without cancelling app shutdown (so don't use "xul-window-registered").
+            nsCOMPtr<nsIAppStartup> appStartup(do_GetService(NS_APPSTARTUP_CONTRACTID));
+            if (appStartup)
+              appStartup->EnterLastWindowClosingSurvivalArea();
+#endif
+
             baseWindow->Destroy();
+          }
         }
       }
     }
@@ -833,7 +847,7 @@ nsMsgComposeService::CacheWindow(nsIDOMWindowInternal *aWindow, PRBool aComposeH
   */
   if (sameTypeId == -1 && oppositeTypeId != -1)
   {
-    CloseWindow(mCachedWindows[oppositeTypeId].window);
+    CloseHiddenCachedWindow(mCachedWindows[oppositeTypeId].window);
     mCachedWindows[oppositeTypeId].Clear();
     
     rv = ShowCachedComposeWindow(aWindow, PR_FALSE);
diff --git a/mailnews/compose/src/nsMsgComposeService.h b/mailnews/compose/src/nsMsgComposeService.h
index 458a9ab11656..c3535403500d 100644
--- a/mailnews/compose/src/nsMsgComposeService.h
+++ b/mailnews/compose/src/nsMsgComposeService.h
@@ -107,7 +107,7 @@ private:
   nsMsgCachedWindowInfo *mCachedWindows;
   
   nsresult OpenWindow( const char *chrome, nsIMsgComposeParams *params);
-  void CloseWindow(nsIDOMWindowInternal *domWindow);
+  void CloseHiddenCachedWindow(nsIDOMWindowInternal *domWindow);
 
   nsresult ShowCachedComposeWindow(nsIDOMWindowInternal *aComposeWindow, PRBool aShow);
 
diff --git a/toolkit/components/startup/src/nsAppStartup.cpp b/toolkit/components/startup/src/nsAppStartup.cpp
index 0a6b83a87300..7f8cff46470c 100644
--- a/toolkit/components/startup/src/nsAppStartup.cpp
+++ b/toolkit/components/startup/src/nsAppStartup.cpp
@@ -365,7 +365,7 @@ nsAppStartup::ExitLastWindowClosingSurvivalArea(void)
   NS_ASSERTION(mConsiderQuitStopper > 0, "consider quit stopper out of bounds");
   --mConsiderQuitStopper;
 
-  if (mRunning && mConsiderQuitStopper == 0)
+  if (!mShuttingDown && mRunning && mConsiderQuitStopper == 0)
     Quit(eAttemptQuit);
 
   return NS_OK;