flake/home/applications/thunderbird/default.nix

{pkgs, ...}: {
  programs.thunderbird = {
    enable = true;
    package = pkgs.thunderbird.override {
      extraPrefsFiles = [
        (pkgs.fetchurl {
          url = "https://raw.githubusercontent.com/HorlogeSkynet/thunderbird-user.js/d6b18302e46349d9924c8a76951bae6efca51501/user.js";
          hash = "sha256-66B1yLQkQnydAUXD7KGt32OhWSYcdWX+BUozrgW9uAg=";
        })
        ./user-overrides.js
      ];
    };
    profiles.default.isDefault = true;
  };
}