Thanks Michael,

Found out that V3 doesn't seem to like the ".js" on the end of "FullScreen.js" for a key command.
But I don't know why or why not it was there. I'm guessing it didn't care in V2.

Okay, noticed a problem with FullScreen.js - on first activation it adds a large blank area to the left of my command pane (which is on the right).
The next activation clears the UI and does what it's supposed to do. The next activation still comes back with the added panel.
You have to re-load MoI to get get rid of it.