Well your user agent is different on each browser...
the user agent helps identify information about the browser..here is an example of mine in google chrome:
Mozilla/5.0 (Windows; U; Windows NT 6.1;
en-US) AppleWebKit/532.5 (KHTML, like Gecko) Chrome/4.1.249.1045 Safari/532.5
notice the "en-US" this tells the website that my language is English..thus the sites can redirect me appropriately
here is a site you can use to check:
http://www.myuseragent.net/