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

https://github.com/zdtcd/void-packages firefox-esr
https://github.com/void-linux/void-packages/pull/14229

Firefox esr
Built and tested for:
- x86_64

Building in progress for:
- x86_64-musl

The language list is updated by this script, and some manual removal:
- https://github.com/zdtcd/xtools/blob/master/xgenlang

A patch file from https://github.com/void-linux/void-packages/pull/14229.patch is attached