Здравствуйте! Почему всплывающее окно прокручивается не плавно? Спасибо :)

#adSite {
width:600px; 
margin-left: 205px;  
position: absolute; 
display:none; 
background:#fff; 
border: 1px solid #ccc; 
padding:15px 10px;
z-index:10000;
}

#adSite .close_line {
color:#CC2D31;
font-family:Arial;
font-size:12px;
line-height:1.5;
text-align:right;
text-transform:uppercase;
}

#adSite .close_line #close_bnt {
bottom:-1px;
margin-left:8px;
position:relative;
cursor:pointer;
}

var block_id = '#adSite';
var top_offset = 100;
var tid = null;
function setCookie(name, value, expires, path, domain, secure) {
	document.cookie = name + "=" + escape(value) +
	((expires) ? "; expires=" + expires : "") +
	((path) ? "; path=" + path : "") +
	((domain) ? "; domain=" + domain : "") +
	((secure) ? "; secure" : "");
}
function getCookie(name) {
	var cookie = " " + document.cookie;
	var search = " " + name + "=";
	var setStr = null;
	var offset = 0;
	var end = 0;
	if (cookie.length > 0) {
		offset = cookie.indexOf(search);
		if (offset != -1) {
			offset += search.length;
			end = cookie.indexOf(";", offset)
			if (end == -1) {
				end = cookie.length;
			}
			setStr = unescape(cookie.substring(offset, end));
		}
	}
	return(setStr);
}
function blockPop() {
	$(block_id).slideUp("normal");
	$(window).unbind("scroll");
	setCookie('pop', '1');
}
document.onkeypress = func;
function func(event) {
	if (window.event) event = window.event;
	var key = event.keyCode ? event.keyCode : event.which ? event.which : null;
	if( (event.ctrlKey) && ( (key == 0xA) || (key == 0xD) ) ) {
		setCookie('pop', '');
		showPop();
	}
}
function showPop() {
	var pop = getCookie('pop');
	if (pop) return;
	setTimeout(function() {
		var win_scrl = $(document).scrollTop();
		var top = parseInt(top_offset + win_scrl);
		$(block_id).css('top', top + 'px').slideDown("normal", function() {
			$(block_id + ' #close_bnt').unbind("click").click(function() {
				blockPop();
			});
			$(window).scroll(function() {
				win_scrl = $(document).scrollTop();
				top = parseInt(top_offset + win_scrl);
				$(block_id).css('top', top + 'px');
			});
		});
	}, 1000);
}
$(document).ready(function() {
	showPop();
});

<div id="adSite">
<div class="close_line"><img height="13" width="13" alt="Close" src="pop_close.gif" id="close_bnt"/></div>
Вот тут информация, которую мы хотим показать в всплывающем окне
</div>