Update Scanner
Open Source
Update Scanner is a Firefox addon to monitor web pages for updates. Useful for websites that don't provide Atom or RSS feeds.
Distill Web Monitor
Freemium
Distill runs in your browser to check monitored pages for changes. Get instant alerts as soon as a change is detected.
Compare WebSite-Watcher with alternatives
Compare Update Scanner and WebSite-Watcher and decide which is most suitable for you.
Compare Distill Web Monitor and WebSite-Watcher and decide which is most suitable for you.