Friction and viscosity refer to forces that oppose the motion.
Main difference
friction is used to refer to forces that resist relative motion, in general,whereasviscosity refers specifically to resistive forces that occur between layers of a fluid when fluids attempt to flow. Therefore, the term “friction” can also refer to resistive forces between solid surfaces, or the resistive forces between solid and fluid surfaces.
Viscous force depends on the velocity gradient and area of contact and frictional force independent of area of contact and relative velocity.
Viscosity of liquid decrease with increase in temperature, Where as friction independent of temperature.