Comment form in wordpress theme returns a javascript alert

I tried removing all the javascript of the theme, updating the comments related files in the server (the same error happens locally)

The problem is a result of this file(you obviously didn’t disable that one in testing).
http://www.faf.fi/wp-content/themes/faf/scripts/js/functions.js

Blocking that script in my browser resolves the issue, but i think it’s this area of the script specifically that’s failing..

    $('form').submit( function(){

        var form = $(this);

        if ( validateForm( this ) ) {

            $.post(
                form.attr('action'),        //url   A string containing the URL to which the request is sent
                form.serialize(),           //data  A map or string that is sent to the server with the request.

                //success   A callback function that is executed if the request succeeds
                function(response, status, request){
                    // do something with response
                    alert( stripTags(response) );
                }

                //dataType  The type of data expected from the server (text, xml, json)
            );
        }
        //Prevent default
        return false;
    });

The alert you’re seeing is generated by that function. I have no idea what the cause of your issue is nor how to resolve it(i’m no JS expert), but i’m pretty certain this function is the source of your problem.

Hope that helps.