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

https://github.com/jnbr/void-packages ff-esr
https://github.com/void-linux/void-packages/pull/15402

firefox-esr: add patch for cssparser
@Piraty 

A patch file from https://github.com/void-linux/void-packages/pull/15402.patch is attached