I rarely saw such original extension like this one, CoBrowse is a very interesting project for education and collaborative browsing firefox extension. With cobrowse installed, one user starts a “server” that will accept incoming connections (currently fixed to port 5000) from folks that have chosen to connect via “client mode”.
The server browser then sends every web page navigation change to every client. It even works when changing tabs!
http://firefox.phpmagazine.net/upload/2006/03/cobrowse-thumb.png
An extension that you must give it a try, it’s very useful for education for example or to help someone in your network browsing online. CoBrowse is written by mark l. chang, you can find FAQs here for more details about how to use this extension. Coming in the next version:
* Multi-user collaboration using a “push-to-talk” navigation scheme… every user can drive
* Preferences pane so you can select a port