  Extremely low density planets ('super-puffs') are a small but intriguing
subset of the transiting planet population. With masses in the super-Earth
range ($1-10$ M$_{\oplus}$) and radii akin to those of giant planets ($>4$
R$_{\oplus}$), their large envelopes may have been accreted beyond the water
snow line and many appear to be susceptible to catastrophic mass loss. Both the
presence of water and the importance of mass loss can be explored using
transmission spectroscopy. Here, we present new HST WFC3 spectroscopy and
updated Kepler transit depth measurements for the super-puff Kepler-79d. We do
not detect any molecular absorption features in the $1.1-1.7$ $\mu$m WFC3
bandpass and the combination of Kepler and WFC3 data are consistent with a flat
line model, indicating the presence of aerosols in the atmosphere. We compare
the shape of Kepler-79d's transmission spectrum to predictions from a
microphysical haze model that incorporates an outward particle flux due to
ongoing mass loss. We find that photochemical hazes offer an attractive
explanation for the observed properties of super-puffs like Kepler-79d, as they
simultaneously render the near-infrared spectrum featureless and reduce the
inferred envelope mass loss rate by moving the measured radius (optical depth
unity surface during transit) to lower pressures. We revisit the broader
question of mass loss rates for super-puffs and find that the age estimates and
mass loss rates for the majority of super-puffs can be reconciled if hazes move
the photosphere from the typically assumed pressure of $\sim 10$ mbar to $\sim
10 \; \mu$bar.
