--- a/toolkit/components/autocomplete/nsAutoCompleteController.cpp
+++ b/toolkit/components/autocomplete/nsAutoCompleteController.cpp
@@ -362,16 +362,23 @@ nsAutoCompleteController::HandleEnter(bo
       int32_t selectedIndex;
       popup->GetSelectedIndex(&selectedIndex);
       *_retval = selectedIndex >= 0;
     }
   }
 
   // Stop the search, and handle the enter.
   StopSearch();
+  // StopSearch() can call PostSearchCleanup() which might result
+  // in a blur event, which could null out mInput, so we need to check it
+  // again.  See bug #408463 for more details
+  if (!mInput) {
+    return NS_OK;
+  }
+
   EnterMatch(aIsPopupSelection, aEvent);
 
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsAutoCompleteController::HandleEscape(bool *_retval)
 {