diff --git a/lib/ace/lib/useragent.js b/lib/ace/lib/useragent.js
index d98e7472..a544c4d1 100644
--- a/lib/ace/lib/useragent.js
+++ b/lib/ace/lib/useragent.js
@@ -60,7 +60,7 @@ exports.isOldIE = exports.isIE && exports.isIE < 9;
 exports.isGecko = exports.isMozilla = window.controllers && window.navigator.product === "Gecko";
 
 /** oldGecko == rev < 2.0 **/
-exports.isOldGecko = exports.isGecko && /rv\:1/.test(navigator.userAgent);
+exports.isOldGecko = exports.isGecko && parseInt((navigator.userAgent.match(/rv\:(\d+)/)||[])[1]) < 4;
 
 /** Is this Opera */
 exports.isOpera = window.opera && Object.prototype.toString.call(window.opera) == "[object Opera]";