[Nico]

I added the missing parenthesis, and it's working fine for me now.

Code:

<script type="text/javascript">
<!--
function popup()
{
    if (confirm('Thank you!')
    {
        window.location = 'http://www.abc.com';
    }
    else
    {
        // User pressed "cancel"... do something?
    }

    return false;
}
//-->
</script>

<a href="#" onclick="return popup();">Click me</a>

Did you change the "Thank you" text to something else?