Recompile DSLinux: Firefox only after boot

I want give users a USB-stick with a bootable Linux on it, which opens [login to view URL] in Firefox. It has to start without user input, configured to eth0 (a working network connection through adsl, cable modem etc.) The user cannot use or see Control Panel, terminal. emelfm, bash, [login to view URL] or any other program. My best guess is to start with DSL or Puppy. DamnSmall Linux is a 50 Mb distro which boots from HD and USB Stick. I want you to recompile the distro to a smaller package. You can upgrade the Firefox 1.0x in the normal distro to a higher version if you want. Your work consists of: 1. getting rid of the unnecessary packages 2. recompile it to a new package 3. some GUI-stuff: user can't see other programs, just Firefox 4. help me with an ISO or whatever so I can put it on an USB stick.