Apple Logic Pro /LogicExpress Discussion

I use my system with a Focusrite Saffire, generally it works fine, but 
sometimes I boot it up, or just wake it from sleep and re-boot logic, 
and I get a nasty digital crackle through the output when I play 
recorded sound or when I input sound. Sometimes the sound disappears 
completely, and once I had bad crackles with about 500ms latency on the 
input signal.
Re-booting Logic doesn't solve the problem. I solved it once after 
several re-starts of the Mac. But what seems to solve the problem is to 
open the Saffire folder in Applications, and run the Firmware Updated.
Then when I re-boot Logic it works fine.
Can anyone tell me what's happening, and what exactly is "firmware", 
and if there's anyway I can avoid this problem.
Thanks,
Tristan.