--- a/layout/generic/nsSelection.cpp
+++ b/layout/generic/nsSelection.cpp
@@ -1088,21 +1088,20 @@ nsFrameSelection::MoveCaret(PRUint32    
 
 NS_IMETHODIMP
 nsTypedSelection::ToString(PRUnichar **aReturn)
 {
   if (!aReturn) {
     return NS_ERROR_NULL_POINTER;
   }
   // We need Flush_Style here to make sure frames have been created for
-  // the selected content.  Use mFrameSelection->GetShell() which returns
-  // null if the Selection has been disconnected (the shell is Destroyed).
-  nsCOMPtr<nsIPresShell> shell =
-    mFrameSelection ? mFrameSelection->GetShell() : nsnull;
-  if (!shell) {
+  // the selected content.
+  nsCOMPtr<nsIPresShell> shell;
+  nsresult rv = GetPresShell(getter_AddRefs(shell));
+  if (NS_FAILED(rv) || !shell) {
     *aReturn = ToNewUnicode(EmptyString());
     return NS_OK;
   }
   shell->FlushPendingNotifications(Flush_Style);
 
   return ToStringWithFormat("text/plain",
                             nsIDocumentEncoder::SkipInvisibleContent,
                             0, aReturn);