fix the space and test with test code below

//var rCSSBindingUrls	= /binding\s*:\s*url\s*\(\s*(?:(['"])|[^'"])([^\1]+)\1\s*\)/g;
var rCSSBindingUrls	= /binding\s*:\s*url\s*\(['"\s]*([^'"\s]+)['"\s]*\)/g;
var aTestStr = [
    'binding: url("ico.xml#bargraph");',
    ' binding : url("ico.xml#bargraph " );',
    'binding : url("ico.xml#bargraph " );',
    'binding: url("ico.xml#bargraph " );',
    'binding:url("ico.xml#bargraph " );',
    ' binding : url (" ico.xml#bargraph " );',
    'binding:url("ico.xml#bargraph " );',
    'binding:url("ico.xml#bargraph" );',
    'binding:url("ico.xml#bargraph");',
    "binding:url('ico.xml#bargraph');"
];

for (var i = 0, iLen = aTestStr.length; i < iLen; i++) {
    console.log(aTestStr[i].match(rCSSBindingUrls), window.RegExp.$1);//window.RegExp.$1);
}

source/xbl.js

@@ -4,7 +4,7 @@
 
 //
 var rCSSRules		= /\s*([^}]+)\s*{([^}]+)}/g,
-	rCSSBindingUrls	= /binding\s*:\s*url\s*\(\s*(?:(['"])|[^'"])([^\1]+)\1\s*\)/g,
+    rCSSBindingUrls	= /binding\s*:\s*url\s*\(['"\s]*([^'"\s]+)['"\s]*\)/g,
 	rCSSComments	= /(\/\*.*?\*\/)/g,
 	rCSSNameSpaces	= /@namespace\s+(\w+)?\s*"([^"]+)";?/g;