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

https://github.com/jnbr/void-packages firefox-75
https://github.com/void-linux/void-packages/pull/20736

[WIP] firefox: update to 75.0.
So far only built for and tested on x86_64-glibc. 

A patch file from https://github.com/void-linux/void-packages/pull/20736.patch is attached