GPG in Thunderbird

I have downloaded the GPG extension (plug-in)
to the Thunderbird mail program.

It is GREAT, works intuitively and exactly as you expect.
The trick is to get it installed.

You can download it from
https://addons.mozilla.org/thunderbird/71/
but DO NOT try to download it using Firefox.
You must follow the instructions (:-)
and download to a local file using Firefox
Then use Thunderbird to import the file.