ShadowFox/css/userContent-files/webextension-tweaks/multiple_tab_handler.css

/*! Alters the webextension Multiple Tab Handler
  IMPORTANT: change the Internal UUID */
@-moz-document url-prefix("moz-extension://multiple_tab_handler_UUID/") {
  h1,
  p,
  ul,
  ul li {
    color: var(--tone-4)!important
  }
}