Whimsy от bwinton

Whimsy is an add-on to help make your Firefox more enjoyable.
It does a variety of things, all toggleable in the addon’s preferences.
Among the more popular features are:

• Replace the tiles on your new tab page with animated gifs!
• Play a coin-collecting sound when you bookmark a page!
• Provide an easy way to load the Cat gifs site.
• …and more!