{...}: {
  programs.firefox = {
    profiles = {
      daniel = {
        userChrome = ''
          #TabsToolbar {
            visibility: collapse;
          }

          #main-window[tabsintitlebar="true"]:not([extradragspace="true"]) #TabsToolbar>.toolbar-items {
            opacity: 0;
            pointer-events: none;
          }

          #main-window:not([tabsintitlebar="true"]) #TabsToolbar {
            visibility: collapse !important;
          }
        '';
      };
    };
  };
}