FireWire

Firewire is popular in the pro-world.

You won’t find many audio devices using Firewire targeting the desktop or the audiophile. A couple of examples can be found here.

FireWire is Apple's trademark for the IEEE 1394 family of standards. FireWire 400 is "S400" IEEE 1394a and is capable of roughly 400 Mbit/sec and uses the rugged 6-pin socket (not the abominable 4-pin socket). FireWire 800 is "bilingual S800" IEEE 1394b-2002 and uses a 9-pin socket.
Source: http://www.teener.com/firewire_FAQ/#Who_invented_Firewire

Apple decided that licence should be $1,- per port.
So industry gave Apple the finger and moved to USB.
Today even Apples leaves out FireWire on some of their new models.

Current offerings by Lynx or RME uses USB instead of Firewire

Makes you wonder if FireWire is the way to go.

FireWire is not jitter free. A good treaty on this subject by Julian Dunn can be found below.

References

Sample clock jitter and real-time audio over the IEEE1394 high performance serial bus -
Julian Dunn, AES 106 May 1999

The Well-Tempered Computer

FireWire