From Active labs:
WhoisLive is a simple add-on that lets you discover and interact with other users who are browsing with you on the same Web page. You can chat, share information or ask questions. Whether you're shopping for a sofa at Ikea.com, reading the news or looking for health or investment advise, WhoisLive is a fun way to meet new people who share your interests.
Wherever you browse:
* Make each Web page a real-life experience
* Interact with anyone in real-time
* Share any online experience with friends