From a Mozilla Blog Post:
Across numerous studies we’ve consistently heard from our users that they want Firefox to protect their privacy on public networks like cafes and airports. With that in mind, over the next few months we will be running an experiment in which we’ll offer a virtual private network (VPN) service to a small group of Firefox users.
This experiment is also important to Mozilla’s future. We believe that an innovative, vibrant, and sustainable Mozilla is critical to the future of the open Internet, and we plan to be here over the long haul. To do that with confidence we also need to have diverse sources of revenue. For some time now Mozilla has largely been funded by our search partnerships. With this VPN experiment which kicks off Wednesday, October 24th, we’re starting the process of exploring new, additional sources of revenue that align with our mission.
Using a VPN service means placing a great deal of trust in its provider because you depend upon both the safety of its technology and its commitment to protecting your privacy. There are many VPN vendors out there, but not all of them are created equal. We knew that we could only offer our users a VPN product if it met or exceeded our most rigorous standards. We also knew that the practices, policies, and character of these vendors would be just as important in our decision.
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Worth Noting: Opera includes free access to a VPN directly from their browser.