  Cosmic infrared background (CIB) includes emissions from objects inaccessible
to current telescopic studies, such as the putative Population III, the first
stars. Recently, strong direct evidence for significant CIB levels produced by
the first stars came from CIB fluctuations discovered in deep Spitzer images.
Such CIB levels should have left a unique absorption feature in the spectra of
high-z GRBs and blazars as suggested in [4]. This is observable with GLAST
sources at z>2 and measuring this absorption will give important information on
energetics and constituents of the first stars era.
