It's modified to have a front-end in a web-browser where you launch the game. And they've already done a lot of the architectural work - the way the game loads - where it's primarily just shifting the file structures and everything, but the game loads very very quickly, so basically you've never played it on a given machine, you can go to the web-browser, click 'play' and almost instantly get into a game.
Though it is loading to your machine in the background, there's not going to be a lot of wait time or an install process and everything.
how do you do quake level 3d graphics and gameplay in a browser?
Like that I guess