I really like this little helper! Rated 5 out of 5 stars
"Semantic Radar is a plug-in for Firefox, notifying the user if it finds SIOC, FOAF or DOAP data referenced by the page he or she is currently viewing. When such data is detected a little icon will appear on the bottom right side of you browser, which lets you access the embedded data easily.
I really like this little helper!"
Peter Scheir - http://blog.scheir.net/2006/08/30/semantic-radar-for-firefox/