Butter a 9x9 baking dish. To easily spread the mixture butter a sheet of waxed paper or use the bag from the cereal if it's empty. In a medium saucepan melt the butter over medium heat. Watching closely, continue to heat the butter until it begins to brown. Reduce the heat to the lowest setting and add the marshmallows. Stir constantly until they are completely melted. Remove pan from heat and add the vanilla and salt. Stir to combine, then add the cereal and quickly stir until well mixed. Turn out into the prepared pan. Using the buttered wax paper spread the mixture into an even layer. Set pan aside to cool mixture. Wait at least one hour for bars to set.