gecko/browser/themes/windows/engineManager.css

%if 0
/* 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/. */
%endif

#engineList treechildren::-moz-tree-image(engineName) {
  -moz-margin-end: 4px;
  -moz-margin-start: 1px;
  width: 16px;
  height: 16px;
}

#engineList treechildren::-moz-tree-row {
  height: 20px;
}