[REGRESSION] "Save link as…" in Firefox no longer works

1 Dec 2025

      I've been testing on the Krita downloads page (it's my normal way of
testing running AppImages).  No more portal save dialog, just nothing.

636a47c9243a8cf0387b6e2e4fbb7d8972e501f4 is the first bad commit
commit 636a47c9243a8cf0387b6e2e4fbb7d8972e501f4
Author: Alyssa Ross <hi@alyssa.is>
Date:   Wed Sep 10 22:06:34 2025 +0200
    lib/nixpkgs.default.nix: update to nixos-unstable-small

    Signed-off-by: Alyssa Ross <hi@alyssa.is>
 host/initramfs/default.nix | 3 ++-
 host/rootfs/default.nix    | 2 +-
 img/app/default.nix        | 2 +-
 lib/nixpkgs.default.nix    | 4 ++--
 vm/sys/net/default.nix     | 2 +-
 5 files changed, 7 insertions(+), 6 deletions(-)

So needs a Nixpkgs bisection.