Easter Eggs are small fun stuffs hidden inside the software, you have to find to get it, or google it. Here is two Easter Eggs from firefox3 . Check them out, they are fun.
Just type in about:robots in the address bar and get a very funny message and a robot pic. It says “Gort! Klaatu barada nikto!” . What is this! This is a phrase originating from the science fiction film The Day the Earth Stood Still . Check the wiki link http://en.wikipedia.org/wiki/Klaatu_barada_nikto .
The page is displayed in the format of Address Not Found page, and has a Try Again button. When you click the Try Again button, the button says : Please so not press this button again. . If you click it again it simply vanishes.
Type in about:robots in the address bar. This will show you the book of Mozilla. Different versions will show different editions. There is no book named “The Book of Mozilla”, this is simply fun, containing quotations from different places. In firefox3 you can see the 11:9 , 10th edition. Check out here in Wikipedia for more: http://en.wikipedia.org/wiki/The_Book_of_Mozilla