firefox does not close window

I use javascript on my vb page,it is working fine in IE and chrome but not in firefox ........

 Page.ClientScript.RegisterStartupScript(Me.GetType(), "asr4", "var win=window.open('','_self');win.close();", True)

I also use

function winClose()
{
window.top.opener=null;
window.close();
}

or

function closeWindow()
{
window.open('','_parent',''); 
window.close();
}

But non of these is working in firefox..............