Rated 3 out of 5 stars
Works as advertised, but with one problem: if you navigate within the tab, or if you reload the tab manually, the countdown is NOT reset. This is a big oversight IMO.
Case in point: I set a tab I work in to be reloaded every 15 minutes (to prevent being disconnected after 20 minutes or so). After about 14 minutes, I happen to navigate to a *new* page within the tab and I begin typing a description in a text area. It's an entirely new page, so technically it has just been loaded, and there's no need to reload it one minute later. But since the countdown hasn't been reset, 1 minute later the tab is reloaded and I loose everything I was typing. This has happened to me several times, and in the end I stopped using this extension.
TL;DR: the countdown should restart every time the page is reloaded (either when manually reloading the page or when navigating to a new page within the tab).