If the temperature of a surface increases significantly, how would this most likely affect the normal force and the frictional force acting on an object resting on that surface?

When the surface gets hotter, the object’s weight and the contact geometry don’t change much, so the normal force stays basically the same. The coefficient of friction, however, usually drops because higher temperatures make the material softer or add a thin film of lubricant, which lowers the microscopic grip between the surfaces. Because frictional force equals the coefficient times the normal force, a lower coefficient means the frictional force decreases. For example, a block resting on a hot metal plate will still be pushed down by gravity, but the sliding resistance will be less than on a cooler plate.