The solution:
If you've installed the XcodeTools package, then paste this into the Terminal.app (/Applications/Utilities/) and see if that makes it visible:
/Developer/Tools/SetFile -a v /
Note that 'Developer/Tools/SetFile -a V / makes the directory invisible and /Developer/Tools/SetFile -a v / will make it visible again. You have to quit the Finder to see its effects. OPT-click on the Finder's dock icon and select relaunch. If that brings the disk icon back to the Desktop, then use this for the FWHD:
/Developer/Tools/SetFile -a v /Volumes/<FireWire disk name>
followed by killing (relaunching) the Finder.
Hope this helps someone, it was a lifesaver for me.
Doug