gecko/browser/base/content/sync/aboutSyncTabs.css

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

richlistitem[type="tab"] {
  -moz-binding: url(chrome://browser/content/sync/aboutSyncTabs-bindings.xml#tab-listing);
}

richlistitem[type="client"] {
  -moz-binding: url(chrome://browser/content/sync/aboutSyncTabs-bindings.xml#client-listing);
}