There is an updated pull request by mmnmnnmnmm against master on the void-packages repository

https://github.com/mmnmnnmnmm/void-packages thunderbird
https://github.com/void-linux/void-packages/pull/24509

[wip] thunderbird: update to 78.2.0
Updated to the 78 branch, this contains big OpenPGP changes and supports only webextensions.

A patch file from https://github.com/void-linux/void-packages/pull/24509.patch is attached