I didn't think that Explorer, and maybe even Mozilla could do an FTP login with a username and password. Looking back at an old install of mine, there's a Step 4 that tells me to FTP in and remove the installation directory.
You'd have to FTP in using the Domain owner you chose in the Panel when you created the Fully Hosted Domain. For quick access, you can go to the DreamHost Panel, under Domains -> Manage Domains and click the WebFTP link to log in. That same Domains screen shows you the username associated with that installation. If you've totally forgotten that user's password, you can reset it under Users -> Manage Users in the panel.