I still haven't figured out how to boot a live Debian usb from Libreboot's menu--selecting "Search ISOLINUX menu (USB)" changes the menu background to a Debian wallpaper, but does nothing else. I think the issue is that at this point Libreboot only supports live usb's created with casper (e.g., Ubuntu, Linux Mint), which Debian doesn't use? Just a guess.
Nevertheless, I found a workaround. When Libreboot's menu comes up, press "c" to enter a grub2 command line. Enter these three commands and you will be able to boot the Debian live USB. linux (usb0)/live/vmlinuz boot=live initrd (usb0)/live/initrd.img boot You may have to confirm that your usb drive is indeed usb0 like mine. To confirm, a simple "ls" (no quotations) at the grub2 command line will help. In my experience (T400 with Libreboot), grub2's ls command and Tab autocompletion take a long time to produce any output (roughly a minute or so), but eventually it does work. Fortunately, a single ls command is all you need to confirm how grub2 sees your usb drive.
