code: public void write() {
      try {
        Wini ini = new Wini(preferenceFile);
  
        for (OperaPreference p : this) {
          ini.put(p.getSection(), p.getKey(), ((AbstractPreference) p).getValue(true));
        }
  
        ini.store(preferenceFile);
      } catch (IOException e) {
        throw new WebDriverException("Unable to write to preference file: " + e.getMessage());
      }
    }
docs: Call this to cause the current preferences representation to be written to disk.  This method
  is called by {@link FilePreference#setValue(Object)} and it is thus not necessary to call this
  method separately unless you wish to perform a forced write of the cache to disk.