This will work for now. In fact that key is already set to "false" in most recent 40.0(.2) release so it will install, but with a warning. But this is going to change. As Mozilla outlined:
"There won’t be any preferences or command line options to disable this." on this blog post:
Granted FiddlerHook isn't required but it sure is helpful, and after using it for so long, programmed into my workflow as it currently works. It would be nice if you guys got it signed.
Just FYI, I'm using latest FiddlerHook 18.104.22.168.
Just FYI 2: The only other option is to move to the Developer Edition (or nightly) as this isn't going to affect them (for obvious reasons).
Regardless, thanks for a great set of tools!