Navigating to http://whatsmyuseragent.com/ shows me my stock Android browser on my Galaxy Nexus running 4.2.1 has the user agent
Mozilla/5.0 (X11; Linux x86_
I need to detect Android Stock Browser to add some custom styles because it doesn't seem to handle box-sizing properly. The code I used is based on @Prakarangs answer which was not working for me. (It did not detect the stock browser on a Galaxy Note 2)
var navU = navigator.userAgent;
var isAndroidMobile = navU.indexOf('Android') > -1 && navU.indexOf('Mozilla/5.0') > -1 && navU.indexOf('AppleWebKit') > -1;
var regExAppleWebKit = new RegExp(/AppleWebKit\/([\d.]+)/);
var resultAppleWebKitRegEx = regExAppleWebKit.exec(navU);
var appleWebKitVersion = (resultAppleWebKitRegEx === null ? null : parseFloat(regExAppleWebKit.exec(navU)[1]));
var isAndroidStockBrowser = isAndroidMobile && (appleWebKitVersion !== null && appleWebKitVersion < 535);
Maybe this is helpful for someone else too.