Bring a large pot of water to a boil. Add salt, lemon, and shrimp. Cook for 2-3 minutes until shrimp turn pink. Drain and rinse with cold water. Pat the shrimp dry with paper towels.
To the bottom of a large bowl, add mayonnaise, lemon juice, Dijon mustard, salt, and pepper. Whisk together. Add shrimp, celery, onion, dill, and parsley. Gently mix together. Taste, and adjust seasoning.
Cover and chill for 1 hour before serving.
*** I cut extra-large shrimp in half when making this salad. Some of the shrimp can be left whole but the larger ones can be cut in half to give a more unified size.