"No problem," I think. "Just update the firmware, that'll probably fix it." The box ships with firmware version 1.01, and firmware 1.02 is out there. But guess what else is broken in 1.01? Yep, firmware update.
In summary, you'll need IE just for a moment to use this thing. Once up to firmware 1.02, though, enabling WEP works in Firefox. Naturally, it's quite possible that newer boxes will ship with 1.02 and Fry's is just unloading the old inventory.