There are multiple Firefly MV models. If you have the model with the 1394 interface, you just need libdc1394. If you have the model with the USB 2.0 interface, you need libdc1394 and libusb. (Interestingly, the USB firefly uses 1394-over-USB in some unholy mixing of standards. But anyway, it works.)
Use MacPorts to install libusb and libdc1394
Download the libdc1394 source (from here).
Run configure in the unpacked libdc1394 directory. It's crucial that your output looks like this:
libraw1394 support (Linux legacy): Disabled (Linux not detected)
Juju support (Linux new): Disabled (Linux not detected)
Mac OS X support: Enabled
Windows support: Disabled (Windows not detected)
IIDC-over-USB support: Enabled
With both Mac OS X support and IIDC-over-USB support Enabled.
Then just run make, and go to the examples directory and use some of the example code. Worked great for me!
(Notes: I'm using OS X 10.6.8 on a MacBook Pro 6,2 (Intel Core i5 2.53 GHz))