{
  pkgs,
  lib,
  config,
  ...
}: let
  lock-false = {
    Value = false;
    Status = "locked";
  };
  lock-true = {
    Value = true;
    Status = "locked";
  };
in {
  # Install firefox.
  programs.firefox = {
    enable = true;
    languagePacks = [
      "ja"
      "tr"
      "en-US"
    ];

    # profiles.osbm = {

    # Check about:policies#documentation for options.
    policies = {
      DisableTelemetry = true;
      DisableFirefoxStudies = true;
      EnableTrackingProtection = {
        Value = true;
        Locked = true;
        Cryptomining = true;
        Fingerprinting = true;
      };
      # DisablePocket = true;
      DisableFirefoxAccounts = true;
      DisableAccounts = true;
      DisableFirefoxScreenshots = true;
      StartPage = "previous-session";
      # OverrideFirstRunPage = "";
      # OverridePostUpdatePage = "";
      # DontCheckDefaultBrowser = true;
      DisplayBookmarksToolbar = "always"; # alternatives: "never" or "newtab"
      # DisplayMenuBar = "default-off"; # alternatives: "always", "never" or "default-on"
      # SearchBar = "unified"; # alternat
      ExtensionSettings = with builtins; let
        extension = shortId: uuid: {
          name = uuid;
          value = {
            install_url = "https://addons.mozilla.org/en-US/firefox/downloads/latest/${shortId}/latest.xpi";
            installation_mode = "normal_installed";
          };
        };
      in
        listToAttrs [
          (extension "tree-style-tab" "treestyletab@piro.sakura.ne.jp")
          (extension "ublock-origin" "uBlock0@raymondhill.net")
          (extension "bitwarden-password-manager" "{446900e4-71c2-419f-a6a7-df9c091e268b}")
          (extension "motivation-new-tab" "")
          (extension "return-youtube-dislikes" "{762f9885-5a13-4abd-9c77-433dcd38b8fd}")

          # (extension "tabliss" "extension@tabliss.io")
          # (extension "umatrix" "uMatrix@raymondhill.net")
          # (extension "libredirect" "7esoorv3@alefvanoon.anonaddy.me")
          # (extension "clearurls" "{74145f27-f039-47ce-a470-a662b129930a}")
        ];
      # To add additional extensions, find it on addons.mozilla.org, find
      # the short ID in the url (like https://addons.mozilla.org/en-US/firefox/addon/!SHORT_ID!/)
      # Then, download the XPI by filling it in to the install_url template, unzip it,
      # run `jq .browser_specific_settings.gecko.id manifest.json` or
      # `jq .applications.gecko.id manifest.json` to get the UUID
    };

    /*
    ---- PREFERENCES ----
    */
    # Check about:config for options.
    preferences = {
      "browser.contentblocking.category" = true;
      "extensions.pocket.enabled" = false;
      "extensions.screenshots.disabled" = true;
      "browser.topsites.contile.enabled" = false;
      "browser.formfill.enable" = false;
      "browser.search.suggest.enabled" = false;
      "browser.search.suggest.enabled.private" = false;
      "browser.urlbar.suggest.searches" = false;
      "browser.urlbar.showSearchSuggestionsFirst" = false;
      "browser.newtabpage.activity-stream.feeds.section.topstories" = false;
      "browser.newtabpage.activity-stream.feeds.snippets" = false;
      "browser.newtabpage.activity-stream.section.highlights.includePocket" = false;
      "browser.newtabpage.activity-stream.section.highlights.includeBookmarks" = false;
      "browser.newtabpage.activity-stream.section.highlights.includeDownloads" = false;
      "browser.newtabpage.activity-stream.section.highlights.includeVisited" = false;
      "browser.newtabpage.activity-stream.showSponsored" = false;
      "browser.newtabpage.activity-stream.system.showSponsored" = false;
      "browser.newtabpage.activity-stream.showSponsoredTopSites" = false;
      "toolkit.legacyUserProfileCustomizations.stylesheets" = true;
      "ui.key.menuAccessKeyFocuses" = false;
    };
  };
}