AutoShutdown works on FF 9 Rated 5 out of 5 stars
Version 0.9.2 of auto Shutdown supports Firefox 9 as from Jan 2012.
The developer must had heard all the pleads. Let's hop he upgrades it to run on FF10. The problem with developers is the frequency of FF updates. Maybe FF need to figure a better way to update the app without a full re-installation.
I usually update the Add-on as soon as a new version of the Add-on-SDK is available. The real problem is Mozilla's verification process. When I upload an new version of the add-on it takes up to four weeks until it's verified and available on this page.