ShadowFox/css/userChrome-files/common_dialog.css

@-moz-document url("chrome://global/content/commonDialog.xul") {
  #commonDialog {
    -moz-appearance: none!important;
    background: var(--in-content-page-background)!important;
    color: var(--in-content-page-color)!important
  }
}