Exploring the very first galaxies is one of the major contemporary problems in astronomy. We do not know when the first galaxies formed, nor how their formation occurred. The James Webb Space Telescope (JWST) will be launched in 2021 and will search for the First Light objects in the redshift range of z=10-15. Reaching these galaxies will be routine with JWST, however, until then, our best chance to study these systems is through deep observations of lensing clusters with the Hubble Space Telescope (HST) by using them as `Cosmic Telescopes'. Therefore, to extend its reach even farther beyond its technical capabilities before JWST is launched, the HST observed six massive clusters of galaxies as gravitational lenses to find the faintest and earliest galaxies in the Universe, ~10-100 times fainter than any previously studied, as a part of the Hubble Frontier Fields (HFF) program. In this talk, I will present how we detect and examine the objects behind HFFs lensing clusters and their parallel fields. We have developed a novel method to subtract the massive galaxies from the clusters, allowing for a deeper and cleaner detection of the faintest systems. We present a photometric study of distant z > 5 galaxies using all 10 bands available for Frontier Fields (HST, Spitzer and K-band). From this, we present new measurements of the evolution of the galaxy stellar mass functions, UV luminosity functions, stellar mass density, UV luminosity density, specific star formation rates and UV spectral slope (β) for galaxies from z=6-9 in the Hubble Frontier Fields. I will further discuss how these results reveal new information on the faint-end of the mass function from the faintest galaxies at high-z, unveiling the potential science that can be done with JWST data.