I have the same problem with the Nexus 7 (2013), which has a front facing and rear camera. Spent literally hours and hours trying to scan the QR code on the web.airdroid.com site. Very frustrating.
You're supposed to enter the 192.168.xxx.xxx:8888 into the browser on your computer not your mobile device. It's the alternative way of establishing a connection between your device and your computer when your device doesn't have a QR Code scanner.