static File mozillaDefaultProfileDir() {
  new Matches m;
  S path = null;
  for (S s : lines(loadTextFile(userDir(".mozilla/firefox/profiles.ini")))) {
    if (startsWith(s, "Path=", m))
      path = m.rest();
    else if (eq(s, "Default=1"))
      ret path == null ? null : userDir(".mozilla/firefox/" + path);
  }
  null;
}