friction force is coefficient of friction multiplied by the normal force. (Fk=Uk M g) . So if coefficient of friction remains the same on another body (if the materials are similar like a certain type of rock), but the gravity is lower, then the normal force will be lower and hence the friction force will be lower. Normal force is gravity multiplied by mass and acts normal to the surface (perpendicular to the surface). So on a slope the normal force will be gravity multiplied by mass multiplied by the Cosine of the angle of the slope. Fk=Uk M g Cos (Theta). So smaller gravity means slippery slopes especially when the gravity is very small like some moons in Kerbin system.