In a large bowl, combine the thawed hash browns with the onions. Mash with a fork until the mixture holds together. Add the salmon, eggs, dill, mustard, pepper and salt, then mix well. Form the mixture into patties, then roll them in the breadcrumbs to coat.
In a large skillet over medium-high, heat the oil. If necessary, use half the oil and cook the patties in batches. Place the patties in the pan and cook until well browned and heated through, 2 to 3 minutes per side. Serve topped with sour cream.