Rated 5 out of 5 stars

Don't bother trying anything in "A possible solution" below...
None of the suggestions will work with this addon, it must be re-authored, and it doesn't look like that's going to happen.
I wish someone would write another add that could do what this
one did, STANDBY, HIBERNATE, or SHUTDOWN various computers/OSs when Firefox has finished with ALL downloads.

This user has a previous review of this add-on.