community/firefox: Add screen sharing with Wayland

Enable pipewire WebRTC supported using a patch from Firefox' flatpak version [1]
which allows screen sharing with Wayland.

Note: This requires the packages `pipewire`, `xdg-desktop-portal`, and some
`xdg-desktop-portal-<BACKEND>` to be both installed and running to work.

parent e3fca97e
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