diff --git a/toolkit/mozapps/extensions/content/extensions.js b/toolkit/mozapps/extensions/content/extensions.js
index 4b13b791c5a2..8e7708f2c876 100644
--- a/toolkit/mozapps/extensions/content/extensions.js
+++ b/toolkit/mozapps/extensions/content/extensions.js
@@ -799,7 +799,7 @@ var gSearchView = {
 
   calculateMatchScore: function(aStr, aQuery, aMultiplier) {
     var score = 0;
-    if (aQuery.length == 0)
+    if (!aStr || aQuery.length == 0)
       return score;
 
     aStr = aStr.trim().toLocaleLowerCase();