Enter Key not firing in Firefox

Hi.

I have an .aspx page that I'm trying to get to fire some Javascript on an Enter Key press inside a text box in a Firefox browser.

Here is the .aspx/html code:

<input type="text" runat="server" id="tbSearch" onkeypress="javascript:SearchEnter();">

And here is the java it's trying to fire:

function SearchEnter()
{

if ( (window.event && window.event.keyCode == 13) || (window.event.charCode == 13))
{
alert("SearchEnter");
SubmitSearch();
}
}

The alert message never appears.

Of course this works fine in IE, just not Firefox.

Any help would be greatly appreciated.

yd