Swarm the dot com

This is a must-have if you like to see what other people are browsing. Using this Firefox extension called Swarm, you can watch what the sites you're browsing and also display what other folks are viewing too. The site describes this app this way:

Swarm is a graphical map of hundreds of websites, all connecting to each other. It updates itself every second with where people are going and coming from. As sites become more popular, they move towards the center of the swarm and grow larger. Conversely, sites that lose traffic move away from the center and grow smaller.

Website traffic is symbolized with thin lines. Each time you see a line appear, it means someone has moved from one site to the other. You can gauge how many people are swarming around based on the number of lines.