In this gist, add 'first-child' class for first-child element. This runs expression only one time. So browser doesn't get slow.

give 'first-child' class in

.someClass{
	behavior: expression(this.style.behavior || ((function(a,b,c){
		c=a.parentNode.getElementsByTagName('!');
		try{for(var i=0,l=c.length;i<l;i++){c[i].parentNode.removeChild(c[i])}}catch(e){};
		if(a.parentNode.firstChild==a){a.className+=' '+b}
	})(this,"lu.first-child"),1));
}