Big fan of Twitch.tv? This add-on lists currently available streams on Twitch.tv as well as letting you save your favorite streamers. Favorites are easier to access and you will be notified when they come online. A search function allows finding of other games and streamers. A dedicated favorites view encompasses all games and shows all favorites together.
For many people, Twitch.tv is a nice way to watch other people live streaming themselves playing games. Here is a little more about Twitch.tv from the developers:
Twitch is home to the most dedicated and highly skilled gamers on the planet. They shatter world records. They cruise through the newest titles. They make headlines with world-first accomplishments, and they make it all look easy. Discover why they’re the best at what they do on Twitch.
One of the only things I can think of that would make the Twitch.tv Stream Browser better would be the ability to show a person even if they are not streaming so you can check out their other content on their channel. Past that, it is perfect.
You can pick up this add-on from the Firefox Add-ons website.