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

https://github.com/jnbr/void-packages firefox_67_0_3
https://github.com/void-linux/void-packages/pull/12536

firefox: update to 67.0.3.
https://www.mozilla.org/en-US/security/advisories/mfsa2019-18/

A patch file from https://github.com/void-linux/void-packages/pull/12536.patch is attached