You can’t use Safari or Netscape to upload files to FTP. While you can enter an FTP location in the address bar, it ends up trying to use the Finder’s built-in FTP client. And for some reason Apple has never allowed users to be able to upload to FTP sites through the Finder FTP, though you can download files. Supposedly Apple doesn’t want users to be confused and use an FTP site as a file management area, but I think if you’re bothering to try to connect to one in the first place then you know what you’re doing. On the Mac you have to use an FTP client to upload files to an anonymous FTP server.