There is a new pull request by pullmoll against master on the void-packages repository

https://github.com/pullmoll/void-packages firefox-esr-78
https://github.com/void-linux/void-packages/pull/26130

[WIP] firefox-esr: update to 78.4.0
Still testing if it builds for all platforms.

A patch file from https://github.com/void-linux/void-packages/pull/26130.patch is attached