Firefox extensions

Many people use the web browser Mozilla Firefox, since it is among the three most popular and is the default on the operating system Linux. So with it's usability comes flexibility and a load of things that can be done with it. There is a page for extensions and themes that are incredibly fun to use.

Nic Cage Addon
Despite the simple name, it may just be one of the most beautiful things ever conceived by man. It replaces every picture on any page with one of Nicolas Cage, and never stops being hilarious.
Get it here

Themes
Moving into a different category, themes are a great way to customize your browser by putting a picture of whatever you want at the top of the browser.