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

https://github.com/oldstager/void-packages fix-firefox
https://github.com/void-linux/void-packages/pull/50453

Fix Firefox so that it doesn't always run in workspace 9
Using default config.h from dwm, every instance of Firefox will **always** run in workspace 9. This patch is used to make dwm run Firefox in current active workspace so that user may run Firefox in any workspace (0-9).

A patch file from https://github.com/void-linux/void-packages/pull/50453.patch is attached