  We derive integral equation for superconducting gap, which takes into account
the quantum nature of electron motion in a parallel magnetic field in a
quasi-two-dimensional (Q2D) superconductor in the presence of a non-zero
perpendicular field component. By comparison of our theoretical results with
the recent experimental data obtained on the NbS$_2$, we show that the orbital
effect against superconductivity partially destroys superconductivity in the
so-called Ginzburg-Landau area of this Q2D conductor, as expected.
Nevertheless, at relatively high magnetic fields, $H \simeq 15 \ T$, the
orbital effect starts to improve the Fulde-Ferrell-Larkin-Ovchinnikov phase in
the NbS$_2$, due to the quantum nature of electron motion in a parallel
magnetic field. In our opinion, this is the most clear demonstration that the
orbital effect against superconductivity in a parallel magnetic field has a
reversible nature.
