How many web browsers do you run? If you're like me, you regularly use Firefox, Internet Explorer, Chrome and Safari. Each of those browsers, of course, has its own underlying rendering engine: Gecko (in Firefox), Trident (in Internet Explorer), and Webkit (in Chrome and Safari). Today, a Japanese startup called Lunascape has released an alpha version of its Lunascape browser, downloadable here, that allows you to switch between all three of these prominent rendering engines. The company says that the Japanese version of Lunascape has been downloaded 10 million times and touts it as the fastest browser available. Is it?