I wonder if the Engine behind it is Open Source or could we use this services from other browsers like Firefox?

This is beneficial for Getting pass Firewall restriction, from China Firewall to Office Internal Firewalls. Speed up Internet connection, especially in places where the shared internet is extremely slow. ( Office or Public Computers )

While i am already using my own VPN for this purpose. It is much slower compared to a normal internet collection if your VPS is not located close to you.