Javascript popup different size in different browsers?

How come this pop-up gets a size other than what I have specified, when testing it in IE6 and FireFox 3.6? Firefox displays it correctly but IE6 is smaller for some reason. (620x530 instead) How can I fix it?

<A id="myID" onclick="windo开发者_运维技巧w.open('/sitecollectiondocuments/myPage.htm',&#13;&#10;'welcome','width=630,height=590')" href="javascript:void(0)"></A>

window.open('/sitecollectiondocuments/myPage.htm','welcome','width=630,height=590').resizeTo(630, 590)