To make programs default in the system, use update-alernatives
For example, to default Google Chrome as the Web Broser, use: 
$ sudo update-alternatives --config x-www-browser

To list all the software with update-alternatives available:
$ update-alternatives --get-selections

To list help:
$ update-alternatives --help

To read any selection configuration:
$ update-alternatives --display x-www-browser

References:
Guide: 3D Acceleration and VR

