Reappearing/appearing div problem

1

ok first heres the javascript

function MM_HideTheAd(){
var theadvert;

theadvert = document.getElementById('thead');
theadvert.style.display = "none";

}

function MM_ShowTheAd(){
var theadvert;

theadvert = document.getElementById('thead');
theadvert.style.display = "block";

}

and the html

<body onload=“MM_HideTheAd()”>
<div class=“thead” id=“thead”>
<object classid=“clsid:D27CDB6E-AE6D-11cf-96B8-444553540000” codebase=“http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,29,0” width=“400” height=“300”>
<param name=“movie” value=“flashadvert/smaller__non__continousrun.swf” />
<param name=“quality” value=“high” />
<embed src=“flashadvert/smaller__non__continousrun.swf” quality=“high” pluginspage=“http://www.macromedia.com/go/getflashplayer” type=“application/x-shockwave-flash” width=“400” height=“300”></embed>
</object>
</div>

The flash movie is hidden at first but then at a certain point in the movie it calls the ShowTheAd function and appears…but only in IE, not in Firefox

anyone any ideas why???