--- a/toolkit/components/autocomplete/nsAutoCompleteController.cpp
+++ b/toolkit/components/autocomplete/nsAutoCompleteController.cpp
@@ -557,18 +557,21 @@ nsAutoCompleteController::HandleKeyNavig
         input->GetTextValue(text);
         input->GetSelectionStart(&start);
         input->GetSelectionEnd(&end);
         if (start != end || end < (int32_t)text.Length())
           *_retval = false;
       }
 #endif
       if (*_retval) {
+        nsAutoString oldSearchString;
         // Open the popup if there has been a previous search, or else kick off a new search
-        if (!mResults.IsEmpty()) {
+        if (!mResults.IsEmpty() &&
+            NS_SUCCEEDED(mResults[0]->GetSearchString(oldSearchString)) &&
+            oldSearchString.Equals(mSearchString, nsCaseInsensitiveStringComparator())) {
           if (mRowCount) {
             OpenPopup();
           }
         } else {
           // Stop all searches in case they are async.
           StopSearch();
 
           if (!mInput) {