A Firefox plug-in that inserts bar charts depicting CO2 emissions data into travel related e-commerce websites. the 1st version visualizes CO2 emissions information to airfare websites such as Orbitz.com, United.com , Delta.com, etc. following versions will work with car directions, car rental, & shipping websites.

http://infosthetics.com/archives/2007/05/real_costs_browser_plugin.html