Is this a new feature on YouTube? I only notice it in one of the video that I watched. It basically darken the background when you the the light down. Maybe it is easier for the viewer to focus on the video when the  turn down the “lights”.

Firefox 3.5 is finally out! You can get it here. Some of the new features in 3.5 are:

• Improved Javascript performance with the new Tracemonkey Javascript engine
• Private browsing
• Tab tearing
• Location aware browsing
• HTML5 video support