Add spamscore header to Thunderbird

As of 2019-02-10 only this plugin / approach seems to work:

"rspamd-spamness" V0.9+

Note: currently V0.9 is not on Thunderbirds Add-Ons site!

Manual Installation

You don't have to wait for release. An XPI file is simply a ZIP file, containing the add-on files. You can just download source files from GitHub and repack them so they are located at the root of the ZIP

Then you can rename it to .xpi or just drag and drop as is to `Add-ons Manager` tab.

Below attached is such a created .xpi V0.9