External iSight not recognized in macOS Sierra

Upgraded to macOS Sierra from El Capitan on my Mac Pro (mid-2010) and everything worked great. However, I noticed Siri could not hear me via my external iSight connected via Firewire.

Then I noticed that the green light wasn't on, and that the iSight was not working at all, or even recognized in System Preferences.

Any ideas on how to make it work?