Boil the shrimp and one of the onions, chopped, in 1 quart of water with the vinegar for 10 minutes. Reserve the water. Peel and clean the shrimp. Cover the rice and okra with one inch of water and cook dry. Fry the remaining onions, finely chopped, in butter over low heat, smooth in the flour, and add the shrimp stock, then the okra, rice, shrimp, tomatoes, and seasoning. Simmer for 20 minutes and serve piping hot.