[protonmail]

You can read about what Mozilla did on their blog post about this: https://blog.mozilla.org/futurereleases/2018/10/22/testing-n...

Quoting from the blog post: "We therefore set out to conduct a thorough evaluation of a long list of market-leading VPN services. Our team looked closely at a wide variety of factors, ranging from the design and implementation of each VPN service and its accompanying software, to the security of the vendor’s own network and internal systems. We examined each vendors’ privacy and data retention policies to ensure they logged as little user data as possible. And we considered numerous other factors, including local privacy laws, company track record, transparency, and quality of support."

It was quite intensive, with on site visits to our office in Geneva and discussions with Mozilla technical leadership.

[codezero]

Thanks, that's what I was looking for!