Javascript
"gathers and reports a computer's IP address; MAC address; open ports; a list of running programs; the operating system type, version and serial number; preferred internet browser and version; the computer's registered owner and registered company name; the current logged-in user name and the last visited URL."
Browser & OS
http://sqa.fyicenter.com/Online_Test_Tools/__Show_Web_Browser_Information.php
Ip address can get got from Javascript.
http://whatismyipaddress.com/
Open ports
http://www.canyouseeme.org/
Mac address:
http://www.devarticles.com/c/a/JavaScript/Advanced-JavaScript-with-Internet-Explorer-Retrieving-Networking-Configuration-Information/1/
It makes no difference if you are behind an anonymizer because Javascript is running on your PC.
So it's a javascript thing.