We have performed a computer simulation study of the force required to slide xenon monolayer and bilayers on a silver surface. With information about the adsorbate-substrate interaction potential deduced from experimental data, we find that for the compressed incommensurate monolayer film the observed sliding friction is very close to the parallel microscopic friction which acts on the individual adsorbates, which is of mainly electronic origin. For the bilayer film a small fraction of the observed sliding friction may arise from internal excitations in the film, and the rest from the direct energy transfer to the substrate via the electronic friction.