Themes (formerly Personas) is a Firefox add-on that allows you to change the look of your browser with easy-to-install, easy-to-use themes. There are thousands of themes to choose from, with more added every day.Discontinued
The URL sends to an Error 404 page. Also, the newest versions of Mozilla now incorporate a new Firefox theme builder add-on: Firefox Color. Here: https://addons.mozilla.org/fr/firefox/addon/firefox-color/
Personas are free, easy-to-install "skins" for Firefox. Personas Plus extends that built-in functionality to give you even more control and easier access to new, popular, and your own favorite Personas.