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

https://github.com/absrd/void-packages firefox-pipewire
https://github.com/void-linux/void-packages/pull/23291

firefox: build with pipewire patch to enable screenshare for wayland users
Enables webrtc pipewire screensharing with pipewire, xdg-desktop-portal and https://github.com/emersion/xdg-desktop-portal-wlr

A patch file from https://github.com/void-linux/void-packages/pull/23291.patch is attached