Cross- Browser machine fingerprinting catches some of the info behind the browser to tag specific machines. Finding graphic card features, cpu and cores, and installed writing scripts
http://yinzhicao.org/
(Cross-)Browser Fingerprinting via OS and Hardware Level Features
Tor blocks most of that info by default, paper says
Fingerprinting a comp behind the browser
Fingerprinting a comp behind the browser
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20130410 Firefox/23.0