Mozilla.com background image. The balloons, flying saucers and birds

If you visit http://www.mozilla.com/en-US/ frequently, you will notice that their background page image will change every time you visit their page. If you reload the same page the background will also change. Here, are the 3 background image of http://www.mozilla.com/en-US/.



I wonder why Mozilla's love balloons, flying saucers and birds

Here's the what's new background image


And the page not found.