I new about one of them for a long time but apparently there are three. Firstly, type "about:mozilla" without quotes in the address bar. You should see a page with a citation from the Book of Mozilla. In Firefox 2 we got this text:
And so at last the beast fell and the unbelievers rejoiced. But all was not lost, for from the ash rose a great bird. The bird gazed down upon the unbelievers and cast fire and thunder upon them. For the beast had been reborn with its strength renewed, and the followers of Mammon cowered in horror.From The Book of Mozilla, 7:15
In Firefox 3b5, the text is different:
Mammon slept. And the beast reborn spread over the earth and its numbers grew legion. And they proclaimed the times and sacrificed crops unto the fire, with the cunning of foxes. And they built a new world in their own image as promised by the sacred words, and spoke of the beast with their children. Mammon awoke, and lo! it was naught but a follower.From The Book of Mozilla, 11:9(10th Edition)
The last egg works only in Firefox 3. Type "about:robots" to get this:
Click on the "Try Again" button for an extra joke..
Bonus: If you have Picasa, open it and press Ctr+Shift+Y. A teddy bear should appear on the screen. Apparently it belongs to one of the developers... if you will continue to press the key combination you will get more teddy bears.