If you are using Personas, a lightweight skin changer for Firefox and are a Harry Potter fan, Warner Bros have released new Harry Potter and Half-Blood prince personas to coincide with the July 15th premier of the movie.
Currently there are 4 personas available in the series, you can see them in action below.
The good thing about using Personas over themes is that you can apply the changes without having to restart the browser.
You will need to install the Personas before you can make use of styles for your browser.
[via Mozilla Links]