First, its a skin for the relatively new web browser Google Chrome. So I hope you have that. If not, you can get it here: [link]
If you're using Chrome, then its just a simple skin. It doesn't slow down browsing - I haven't used any HD textures or anything, its all rather reasonable providing you have a average PC.
To install the skin in Chrome, simply download the file, unzip it with a suitable file extraction tool and drag it from the desktop onto an open chrome window, it will then present a message asking you whether you want to install the skin.