After I updated OS9.1 on my G4 to OS9.21, the Que firewire CD burner connected to it failed to be recognized. Here's what I did and it worked. Now my Que CD drive is recognized as it should be. The remedy may not be fool-proof or universal and it may even be totally irrelevant. But, hey, it did the trick for me.

What I yanked out of the Extensions Folder

Apple Packet Media Access
Authoring Support
Authoring Support Files
Disk Burner Extensions
FireWire Authoring Support
iTunes Extension
SDAP Authoring Support
USB Authoring Support

The following files stay put in the Extensions Folder

Apple CD/DVD Driver
FireWire Enabler
FireWire Support
Toast CD Reader
Toast FireWire Support