Answer the question and give example: can friction ever perform positive work?

Yes. Think of block sitting on top of a bigger block. If the bottom block moves, it will drag the top block with it. Since the force of friction on the small block and its displacement are in the same direction, the "work" is positive. The static friction is a passive force, It is not a source of energy; it transmits the force placed on the bottom block. (And the "work" done by the friction on the bottom block is exactly the negative of the work done on the top block.) 

It do both Positive and Negative work.
If we have to stop some object then friction does a positive work.
For Example: to stop a car , necassary friction is required between the tyres of car and road to stop a car .