Experimenting with AR on the mobile Web using getUserMedia and A-Frame, the declarative VR library from Mozilla.
VIEW DEMO (requires Firefox on Android)
How It Works
I used the getUserMedia API to get access to the phone's camera stream, and set that stream as the background of the entire page. Then I create an A-Frame scene above it, with no background.
NOTE to iPhone/iPad users
Apple chose to not implement the getUserMedia API, so this will not work on iOS or Safari. Let Apple know that you want a better mobile web on iOS devices by filing a request with Apple.

As a developer:
Geolocation
Fun additions
This is a technology demo. Feel free to fork and improve or use however you like.
I wrote this as an example of what is possible. I might take pull-requests or augment the code based on pull-requests, but currently have no plans to turn this into a full-featured AR web solution at this time.