I can connect the drive via USB and it mounts correctly. However, when I connect via FireWire, the drive powers down.
The drive realizes that it is plugged in. When I plug in via FireWire, the lights on the front of the drive flash the same as when it it mounting via USB, but then the drive powers down. I've upgraded the firmware on the drive, but it still won't mount via FireWire.
Edit: After a relatively painless RMA process, I got a new drive from Western Digital and it is working on my Macbook via FireWire.