Did you try removing ZStartwAHK.ztm and FF.EXE out of the equation? I don't
use ZBarFileInfo, so I can't help you with reproducing.
By the way, I start FF.EXE on boot by putting it in the Startup folder, not
launching it from ZTW. That's my choice; it's an idependent process and does not need to be started from ZTW.
AutoHotkey is no longer so stable for me either, on Windows 8.1. Every few days,
FF.EXE and one other AHK script I always launch stop working after some unidentified
system event, or my action on my PC. I have to right-click their tray icons and
perform a "Reload This Script" to get them to work.
I'm too lazy to investigate and/or migrate AHK to the new, object-oriented, implementation.