  We use the time-dependent Bogoliubov de Gennes equations to study dark
solitons in three-dimensional spin-imbalanced superfluid Fermi gases. We
explore how the shape and dynamics of dark solitons are altered by the presence
of excess unpaired spins which fill their low-density core. The unpaired
particles broaden the solitons and suppress the transverse snake instability.
We discuss ways of observing these phenomena in cold atom experiments.
