How does facebook rewrite the source URL of a page in the browser address bar?

Go to http://www.facebook.com/facebook?v=wall, then click on the info tab. The content will be loaded, and the address bar now becomes http://www.facebook.com/facebook?v=info but the webpage didn't reload.

At first I think it is Ajax, but my question is, how do you change the address bar without reloading? I know I can change anchor (#wall) using JS but querystring (?v=wall), how?