Of course, the app is only a first version, and it has a lot of potential for improvement. You can get the Tutanota app directly from the Firefox Marketplace. It would be great if you start using it right away so that you can give feedback.
We want to thank Nino Vranešič for his support and commitment in pushing the Tutanota app on the Firefox Marketplace. Without Nino we wouldn't have succeeded so quickly.
Since we have published the Tutanota apps for Android and iOS almost one year ago, we wanted to make them available to more communities, particularly to people who use other devices than Android or iOS for privacy reasons. Plus, being the first open source secure email service available on Firefox OS makes us very proud!
Tutanota Web app for Ubuntu
We would also love to put the Tutanota app on F-Droid, but haven't succeeded so far.