The popular Firefox web browser has a few "hidden" features accessed by the " about: " URL. MozillaZine has an article about them and the actual code can be viewed here . The about:robots URL is an Easter Egg, or hidden joke. Another Easter Egg was attempted but was thwarted: someone wanted to include an about:kitchensink joke. There is a humorous discussion here (Comments #119 and #120 are the most important) and you can see a demonstration of the joke here . If you are interested, there are several about: extensions available for Firefox here .