First there is no Java on the page. Just a form.

> I've done even what's written in 
> <http://www.httrack.com/html/addurl.html>
Adding a url has nothing to do with authentication

> and I've got the confirmation page on my Firefox...
Authentication in FF doesn't mean httrack has logged in

Form-based authentication -
<http://httrack.kauler.com/help/Form-based_authentication>

Don't forget to filter out the log out url if any.