if(typeof(HTMLElement)!="undefined" && !window.opera) 
{ 
    HTMLElement.prototype.__defineGetter__("outerHTML",function() 
    { 
        var a=this.attributes, str="<"+this.tagName, i=0;for(;i<a.length;i++) 
        if(a[i].specified) 
            str+=" "+a[i].name+'="'+a[i].value+'"'; 
        if(!this.canHaveChildren) 
            return str+" />"; 
        return str+">"+this.innerHTML+"</"+this.tagName+">"; 
    }); 
    HTMLElement.prototype.__defineSetter__("outerHTML",function(s) 
    { 
        var r = this.ownerDocument.createRange(); 
        r.setStartBefore(this); 
        var df = r.createContextualFragment(s); 
        this.parentNode.replaceChild(df, this); 
        return s; 
    }); 
    HTMLElement.prototype.__defineGetter__("canHaveChildren",function() 
    { 
        return !/^(area|base|basefont|col|frame|hr|img|br|input|isindex|link|meta|param)$/.test(this.tagName.toLowerCase()); 
    }); 
}

<div id="test">
   <input type="text" name="text" />
   <p>this is a sentence</p>
</div>

<script>
var out = document.getElementById("test").outerHTML;
</script>