p≡p for Thunderbird consists of several components.
The p≡p for Thunderbird add-on component works in all modern versions of Thunderbird, that is Thunderbird v68 and v78.
The add-on itself, which is visible in Thunderbird 68 and 78 under the "Add-ons" area of Thunderbird, can be found (for now) on a mercurial instance of p≡p security:
hg clone https://pep-security.lu/dev/repos/pEp_for_Thunderbird/
The core functionality of p≡p is processed by the p≡p JSON Server Adapter, which is a software component provided by the p≡p foundation. This component also includes Sequoia PGP -- the OpenPGP backend which is used by all modern p≡p products. Learn more about Sequoia PGP and get involved here: https://sequoia-pgp.org/
hg clone https://pep.foundation/dev/repos/pEpJSONServerAdapter/