1. Mix tomatoes, sugar, and salt in a large bowl.
2. Peel lemons and oranges. Boil peel for 8 minutes in enough water to cover. Drain off and discard the water. Cut peel into thin strips.
3. Slice lemon and orange pulp very thin and remove seeds.
4. Combine peel, citrus pulp, and tomato mixture in a large kettle. Heat to boiling and cook rapidly, stirring constantly until thickened, about 45 minutes.
5. Pour into sterilized jars and seal. Process in boiling water bath for 10 minutes.