Combine flour, salt, pepper and paprika. Put flour mixture in a plastic bag. Shake the ribs in the bag, two at a time. Brown in oil on all sides in a frying pan. Remove to casserole.
Chop the onion into large chunks and place on top of browned ribs.
Whisk the tomatoes, barbecue sauce, molasses and cider vinegar together. Pour over the ribs and onions. Cover and bake at 275F (135C) for 3 - 4 hours. Serve with mashed potatoes.