Did you know there’s a Lightning Beta available on the developer channel on AMO for Thunderbird Betas?
No? Well there is.
If you’re running, or wanting to run Thunderbird Beta builds and you want Lightning as well, then head over to the Lightning page on AMO and scroll down to the bottom – you’ll see the Development Channel which is what you want to download and install into your Thunderbird Beta.
Once you’ve done that, updates are automatic. Whenever a new Lightning Beta build is out you’ll get it. No more needing to download special builds.
The Lightning folks are working to ensure that whenever a new beta version of Thunderbird is released, there will be a Lightning Beta compatible with it.