diff --git a/include/util.js b/include/util.js
index 272da9aa68e620eb34c961750acb538246cff2b6..b67391d1f5ede954c12ace588064d60ebd1a3c74 100644
--- a/include/util.js
+++ b/include/util.js
@@ -244,7 +244,7 @@ Util.Engine = {
     //'webkit': (function() {
     //        return ((typeof navigator.taintEnabled !== "unknown") && navigator.taintEnabled) ? false : ((Util.Features.xpath) ? ((Util.Features.query) ? 525 : 420) : 419); }()),
     'gecko': (function() {
-            return (!document.getBoxObjectFor && !window.mozInnerScreenX) ? false : ((document.getElementsByClassName) ? 19 : 18); }())
+            return (!document.getBoxObjectFor && window.mozInnerScreenX == null) ? false : ((document.getElementsByClassName) ? 19 : 18); }())
 };
 
 Util.Flash = (function(){