Hi Joe,
I didn't use an FTP addon to Firefox. I used the standard browser. All internet browsers are actually capable of FTP. You know how website addresses all start with http://? Most people probably think that's a pointless waste of characters since every page they ever access has the same ones. But it actually does mean something.
Start with FTP:// and then put the domain name you picked at dyndns.org, and you will FTP to the router. I don't think this method of FTP really has a good way to upload files to the FTP server, but it works okay for viewing directories, retrieving files from the FTP server, etc. Filezilla is a better FTP client - I'm not dissing on it. I'm just describing how to reproduce how I got media files to stream and play on a remote computer outside the network with my DNS-323.
Okay. So that's how you connect. You also need to make sure you have the FTP server on the DNS-323 setup correctly. You need to setup a user account and then give it access to the right directories under the FTP server setup page.
Another interesting point is that this streaming ability seems to work using quicktime for audio files but when I try to stream video files to quicktime or media player it doesn't seem to stream, ie it downloads the file entirely before beginning playback. So I've got streaming working to external devices for audio but not for video.