static File mozillaDefaultProfileDir() {
  File base = mozillaConfigBaseDir();
  new Matches m;
  S path = null;
  for (S s : lines(loadTextFile(newFile(base, "profiles.ini")))) {
    // TODO: Does IsRelative=0 work?
    if (startsWith(s, "Path=", m))
      path = m.rest();
    else if (eq(s, "Default=1"))
      ret path == null ? null : isAbsolutePath(path) ? newFile(path) : newFile(base, path);
  }
  null;
}