They've recently add a bunch of new Firefox Sports Themes (mostly football) so that your browser can be more sports oriented. Many were just added in the last half of July. Hopefully many more will be added (there were 14 sports themes to choose from at last count). Here's there current list:

Super Chargers - a San Diego Super Chargers theme
Chicago Bears
Washington Redskins
New Orleans Saints
FriarFox - a San Diego Padres theme
Washington Capitals
Everything Elio - a Firefox theme for fans of Italian F1 driver Elio De Angelis and the JPS Team Lotus
Chargers 2007 - a San Diego Super Chargers theme
RedSoxfox
Packerfox
Arizona Wildcats
Broncofox
KC Chiefs
Patriotfox

Hopefully, these themes will work with whatever version of Firefox you use.