In this work we report very accurate variational calculations of the twelve lowest S-2 Rydberg states of the lithium atom performed with the finite-nuclear-mass (FNM) approach and with all-electron explicitly correlated Gaussian functions. The FNM non-relativistic variational energies of the states are augmented with the leading relativistic and QED corrections. The calculated transition energies are compared with the previous works (only eight states of the series were calculated before) and with the available experimental results. Density distributions of the electrons and the nucleus in the center-of-mass frame are also shown.