0. Compile a new kernel with 

CONFIG_LIBERTAS_THINFIRM=m
CONFIG_LIBERTAS_THINFIRM_USB=m

1. Install firmware 

# wget http://dev.laptop.org/pub/firmware/libertas/thinfirm/lbtf_usb.bin
# cp lbtf_usb.bin /var/lib/firmware/lbtf_usb.bin

2. Switch drivers

# rmmod usb8xxx libertas
# modprobe libertastf_usb

3. Bring up the interface

# ifconfig wlan0 up
# iwconfig wlan0 essid whatever
# dhclient wlan0

4. Use it

# lynx dev.laptop.org