Please post what you did, for the records and future searchers.
From my working Linux box I copied again /etc/cups/printers.conf to /usr/local/etc/cups. Before that I upgraded to
TCL-4.5.5 and to Firefox-13.0.1. Opening cups Add Printer, there, suddenly was "usb://Unknown/" which is my Epson printer DeviceUri.
From my experiences in other distros it does happen that this usb://Unknown/ will not show and then suddenly it does, however,
copying printers.conf with this DeviceUri usually works. Not so earlier in TCL.
EDIT: I almost will belive that the working of my Epson printer now has something to do with the TCL version.
I installed now on my flashdrive TCL-4.5.6 and there now as well the Epson printer is detected, whereas it was not with 4.5.4.