  We use one-dimensional radiative transfer simulations to study the evolution
of H_2 gas-phase (H^- catalyzed) formation and photo-dissociation regions in
the primordial universe. We find a new positive feedback mechanism capable of
producing shells of H_2 in the intergalactic medium, which are optically thick
in some Lyman-Werner bands. While these shells exist, this feedback effect is
important in reducing the H_2 dissociating background flux and the size of
photo-dissociation spheres around each luminous object. The maximum background
opacity of the IGM in the H_2 Lyman-Werner bands is \tau_{H_2} ~ 1-2 for a
relic molecular fraction x_{H_2}=2 x 10^{-6}, about 6 times greater than found
by Haiman, Abel & Rees. Therefore, the relic molecular hydrogen can decrease
the photo-dissociation rate by about an order of magnitude. The problem is
relevant to the formation of small primordial galaxies with masses M_{DM} <
10^8 M_\odot, that rely on molecular hydrogen cooling to collapse.
Alternatively, the universe may have remained dark for several hundred million
years after the birth of the first stars, until galaxies with virial
temperature T_{vir} > 10^4 K formed.
