Vincent from our page for FAN:
If you are tired of seeing the same skin (theme) of Facebook everyday, here are two alternatives that allow you to choose from hundreds of different themes to personalize your Facebook. These extensions are not developed by Facebook and all skins are for your viewing only.
1. PageRange lets you choose from a large database, that has many categories, that will help you choose the perfect skin. Once you find it, download and install the plugin. Then click on "Install Free Plug-in" and follow the instructions on the page. Pagerang supports Firefox 3 and Internet Explorer.
2. Userstyles.org lets you choose between different skins for popular sites such as Facebook. Depending on which browser you are using, follow the instructions in the green box in the upper right "How to install".