NixOS: Firefox in distrobox does not use Adwiata theme (no hand mouse cursor)

NixOS injects its Nix store paths into XCURSOR_PATH so the host system finds cursors in /nix/store/..., and distrobox inherits that variable. Inside the Arch container those paths don't exist, so libxcursor found nothing and silently fell back to the default arrow for every cursor change.
vim .config/fish/config.fish
set -e XCURSOR_PATH
set -x XCURSOR_PATH /usr/share/icons ~/.icons


When creating launcher for firefox in xfce4, have to reset `XCURSOR_PATH`:
/run/current-system/sw/bin/distrobox-enter -n abox -- bash -c 'XCURSOR_PATH=/usr/share/icons /usr/lib/firefox/firefox %u '