I'm not sure I recognize a problem. The server (vsftpd) sounds like it is working. The client you are using determines the login method and most browsers (IE and firefox, in your example) offer some method of auto-anonymous login attempt. In you case, they succeed and are placed in, most likely, /var/ftp/. Depending on the client and the features offered, you may be able to set user and/or user
ass as demonstrated in your example above.
Are you not wanting anonymous ftp login at all?
If you wish to deny anonymous-user ftp access you may look at man 5 vsftpd.conf
Controls whether anonymous logins are permitted or not. If
enabled, both the usernames ftp and anonymous are recognised as