Define feedforward system, define absolute stable...
Commonly, ffwd system means an open loop control system without any feed back. As far as I'm aware of, "absolute stability" is an algebraic rather than control theory term. In so far I'm not sure what's it's expected to mean in this context.
For control system analysis, we can e.g. refer to BIBO (bounded in - bounded out) stability. We must obviously presume that the "controller" (compensator, whatsoever) must be BIBO stable, e.g. not contain poles in the origin. The same must be demanded for the plant.