{
  pkgs,
  lib,
  sLib,
  info,
  ...
}:

let
  submodule =
    { name, ... }:
    {
      options = {
        packages = lib.mkOption {
          type =
            sLib.compose
              [
                lib.types.listOf
                (lib.types.either lib.types.package)
                (lib.types.submodule)
              ]
              {
                options = {
                  name = lib.mkOption {
                    type = lib.types.str;
                    default = name;
                    example = "ublock-origin";
                    description = "The short name of the extension. To find the short name look at the extension's download link.";
                  };

                  guid = lib.mkOption {
                    type = lib.types.str;
                    example = "uBlock0@raymondhill.net";
                    description = "The guid of the extension. To find the guid go to https://addons.mozilla.org/api/v5/addons/addon/\${shortName}/";
                  };
                };
              };
          default = [ ];
          description = ''
            Extensions to install for this profile. Takes either a package or a description of an extension.
            * If a package is given, the extension will be preinstalled.
            * If a description is given then ${info.name} will download the extension on startup.
          '';
        };

        settings = lib.mkOption {
          type =
            let
              jsonFormat = pkgs.formats.json { };
            in
            lib.types.attrsOf jsonFormat.type;
          default = { };
          description = "Settings for this extension, accessible by the managed storage API. The extension must be referenced by id.";
        };
      };
    };

  # (Package -> a) -> ({ name, guid } -> a) -> Extension -> a
  withExtension =
    f: g: x:
    if lib.isDerivation x then f x else g x;

  # ublock-origin wants its settings as a string, which is annoying
  # to merge. For convenience, you can keep ublock-origin's config
  # as a set and this function will turn it into a string at the
  # last minute. As a bonus, we can also do other magic for other
  # extensions if need be.
  magicInfo = {
    "uBlock0@raymondhill.net" =
      x:
      x
      // lib.optionalAttrs (x ? adminSettings) {
        adminSettings = sLib.compose [
          builtins.toJSON
          (
            y:
            y
            // lib.optionalAttrs (y ? userFilters) {
              userFilters = builtins.concatStringsSep "\n" y.userFilters;
            }
          )
          (
            y:
            y
            // lib.optionalAttrs (y ? urlFilteringString) {
              urlFilteringString = builtins.concatStringsSep "\n" y.urlFilteringString;
            }
          )
          (
            y:
            y
            // lib.optionalAttrs (y ? hostnameSwitchesString) {
              hostnameSwitchesString = builtins.concatStringsSep "\n" y.hostnameSwitchesString;
            }
          )
          (
            y:
            y
            // lib.optionalAttrs (y ? dynamicFilteringString) {
              dynamicFilteringString = builtins.concatStringsSep "\n" y.dynamicFilteringString;
            }
          )
        ] x.adminSettings;
      };
  };
  magic = guid: magicInfo.${guid} or lib.trivial.id;
in
{
  options = {
    extensions = lib.mkOption {
      type = lib.types.submodule submodule;
      default = { };
      #      example = {
      #        packages = [
      #          nur.repos.rycee.firefox-addons.ublock-origin
      #          { name = "decentraleyes"; guid = "jid1-BoFifL9Vbdl2zQ@jetpack"; }
      #        ];
      #        settings."uBlock0@raymondhill.net" = {
      #          whitelist = [ "example.org" ];
      #        };
      #      };
      description = "The extensions to install.";
    };
  };

  process =
    { extensions, ... }:
    {
      policies = {
        "3rdparty".Extensions = extensions.settings;
        ExtensionSettings = sLib.compose [
          builtins.listToAttrs
          (builtins.map (
            withExtension
              (x: {
                name = x.addonId;
                value = {
                  installation_mode = "force_installed";
                  private_browsing = true;
                  install_url = "file://${x}/share/mozilla/extensions/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}/${x.addonId}.xpi";
                };
              })
              (x: {
                name = x.guid;
                value = {
                  installation_mode = "force_installed";
                  private_browsing = true;
                  install_url = "https://addons.mozilla.org/firefox/downloads/latest/${x.name}/latest.xpi";
                };
              })
          ))
        ] extensions.packages;
      };
      prefs."extensions.autoDisableScopes" = 0;
    };

  postprocess =
    { policies, ... }:
    lib.optionalAttrs (policies ? "3rdparty".Extensions) {
      policies."3rdparty".Extensions = builtins.mapAttrs magic (policies."3rdparty".Extensions or { });
    };
}