This started happening today. Each watcher will trigger the alert one time. After that it never alerts again. I have found two ways around this:
1. Shut firefox down for 10 minutes or so, fire it back up. This will then allow each watcher to alert one time again.
2. Remove and reinstall the script (of course backing up and reinstalling watchers), this too will allow each watcher to alert one time.
I tried installing it in chrome also, but the same behavior persists.
I have been using TurkMaster for about one month with no issues at all.