When originally looking into wireless bootloading using XBee, I found this article on the Ladyada site extremely useful. Here are the steps you need to configure for Firewing. It assumes you are using the X-CTU configuration software, connected to a Sparkfun Explorer Board. Please note that an equivalent host board should work just as well.

Pan ID

This should be a four digit hexadecimal number. Both the transmitter and receiver must have matching IDs

Interface Data Rate

The Firewing XBee loader uses a baudrate of 38400

Packetization Timeout

This value is taken directly from the Ladyada site and works very well with the Firewing loader. It basically determines the timeout value between transmission characters.

D3 Input / Output Pin

This pin is hardwired to the explorer board DTR pin, which controls software reset. It needs to be configured as an input.

Change Detect

Again this value is taken directly from the Ladyada site and works well. It's simply a mask value but given that we are using only one XBee pin (DIO3) it can be set to FF

Don't forget to press the X-CTU "Write" button after making all of the changes!