How to update external iSight firmware?
Apple released an iSight Updater software package, which is still available online:

iSight Updater 1.0.3
https://support.apple.com/kb/DL502

The problem is that the software download requires Mac OS X v10.3 Panther to run.
iSight can also be updated on OS X 10.4 Tiger and 10.5 Leopard. The updater on those systems is located at:
\System\Library\CoreServices\iSight Updaters\iSight Updater
So, find an OS X 10.3, 10.4, or 10.5 machine or VM to run the iSight Updater software.