OWA stands for Outlook Web Access. It is a mean of gaining access to an Exchange account through web browser. That is what it is, to allow users of Microsoft Exchange services to access their accounts without having to go through the hassle of setting up and configuring client softwares. In other words, use Firefox to log in through OWA.
If you want to access your Exchange account using a client software, you have to try Evolution instead. That is what I use to take advantage of a telco-deployed Exchange service here. And there is no way we can tell what the correct settings should be like, since we are not the ones who roll out the service. You really have to consult the people who are in charge of it.