Great extension given the workarounds that are needed to make this work as webextension (which is needed for FF 57+).

However, the "check connection page" which you get pressing Open on settings page might be misleading, if it claims that " If you still get this page even when the "Check Button" reports successful connection, it means the application cannot be accessed (path is not correct in the options page)", since Auto Shutdown might still work.

Set shutdown /s /f /t 120 (on windows) to have two minutes to cancel the shutdown with shutdown /a in a command window.

Hint: Author replies fast on https://github.com/andy-portmen/auto-shutdown/issues