Preheat the oven to 350 degrees F.
Arrange the ribs meaty side up in 1 layer in lightly oiled baking pans and season with salt. Bake until slightly tender, about 20 to 30 minutes.
Meanwhile in a large bowl, combine the beer, soy sauce, mustard, sugar, onion, and Worcestershire sauce.
Cut the ribs into 1-rib sections, add them to the bowl, stirring to coat them with the marinade, and let them marinate, covered, at room temperature, stirring occasionally, for 2 hours or chill them, covered, overnight.
Remove the ribs from the marinade, reserve marinade, and arrange them meaty side-up in one layer in lightly oiled baking pans. Bring marinade to a boil and brush the ribs with some of the marinade, and bake in a preheated 350 degree F. oven, turning and basting them occasionally, for 1 hour, or until they are tender and glazed. (The ribs may be baked 1 day ahead and chilled, covered. Reheat the ribs in baking pans in a preheated 350 degree F. oven for 10 to 15 minutes, or until they are heated through.) Serve the ribs warm or at room temperature and garnish them with the scallions, if desired.