App
Lots of minor bugs and glitches are fixed, too many to name here. All in all the app looks pretty mature, only minor bugs have been reported so far. So time to make this the first official release.
Be aware of one breaking change. In order to have a common codebase with the webextension the account settings needed to be changed. Which means you need to recreate all of your accounts.
Noteworthy is importing Thunderbird's accounts settings on Linux was fixed by Jonas Bögle and a macOS packaging step was contributed by Eduard Martinescu.
In case you stumbled upon a bug or have a feature request please report it.
In case you are looking for a macOS build, you need to test and build it on your own. I don't own a mac, so I can not test or support macOS builds.
As before keep in mind the app will not update automatically.
WebExtension
The experiment evolved and this release will be the WebExtension's first official pre-release.
It is still very rough so don't expect too much. Especially as WebExtension are limited by design, there is nothing to do about this, so it can never reach parity with the app.
The future is still very unpredictable. Until now there is no official announcement from the Thunderbird Project if WebExtensions Experiment will stay enabled with future Thunderbird Releases.
I will try to upload it to addons.thunderbird.net, but as this was a huge rewrite, the mandatory review will most likely take several weeks.
Noteworthy Stuff
The project has now an shiny new icon!
It is a commercial icon bought from donations and has a good quality. But the icon's license is sadly non exclusive, neither free nor open and usage is bound strictly to this project. So no reuse outside this code base is allowed or possible.