Place chicken thighs, chicken feet, vinegar, onions, carrots and celery in a large soup pot. Add enough water to cover all the bones. Let sit for 30 minutes to an hour. Bring to a boil, then reduce heat to low; cover and simmer for 6-8 hours, removing scum that floats to the top occasionally. Add parsley and let simmer another 10-15 minutes. Let cool; then strain broth.