Hacker News Reader

Yes! https://mullvad.net/en/blog/2019/12/3/mullvad-partnerships-p...

Yes, they are. They are also listed on their "Partner and Reseller" page: https://mullvad.net/en/help/partnerships-and-resellers/

Mozilla partnered with ProtonVPN, which also makes ProtonMail.

In 2018. I think they're no longer parterned, or at the very least Firefox no longer has that popup recommending ProtonVPN to users ever since the new partnership with Mullvad.