static File mozillaConfigBaseDir() {
  if (isWindows())
    ret newFile(newFile(System.getenv("APPDATA")), "Mozilla/Firefox");
  else if (isMac())
    ret oneOfTheDirs(
      userDir("Library/Application Support/Firefox"),
      userDir("Library/Mozilla/Firefox")); 
  else
    ret userDir(".mozilla/firefox");
}