  In the series of recent publications we have proposed a novel approach to the
classification of integrable differential/difference equations in 3D based on
the requirement that hydrodynamic reductions of the corresponding
dispersionless limits are `inherited' by the dispersive equations. In this
paper we extend this to the fully discrete case. Our only constraint is that
the initial ansatz possesses a non-degenerate dispersionless limit (this is the
case for all known Hirota-type equations). Based on the method of deformations
of hydrodynamic reductions, we classify discrete 3D integrable Hirota-type
equations within various particularly interesting subclasses. Our method can be
viewed as an alternative to the conventional multi-dimensional consistency
approach.
