It uses the latest version of css_browser_selector published by Andrew Relkin on GitHub as far as the original mantainer has not updated the product for some time.
The original author of css_browser_selector is Rafael Lima (http://rafael.adm.br)
Credit is given according to the original file’s CC-BY license
The products contains both the original version of the js file and also a minified version created by YUI-compressor 2.4.7
The JS added to Plone is the minified one.