Season ribs with salt and pepper to taste. In a large skillet, over medium-high heat, brown ribs on all sides.
Place half of the onion, green pepper, and celery in the bottom of a slow cooker. Place half of the ribs on top the vegetables, then repeat layering with the remaining vegetables and ribs. In a medium bowl, stir together the tomato sauce, brown sugar, vinegar, lemon juice, and Worcestershire sauce. Pour mixture over the top of the ribs.
Cover, and cook on High for 1 hour. Reduce to Low, and cook for another 8 to 9 hours.