  The properties of warm-hot gas around $\sim L_{*}$ galaxies can be studied
with absorption lines from highly ionized metals. We predict Ne VIII column
densities from cosmological zoom-in simulations of halos with masses in $\sim
10^{12}$ and $\sim 10^{13}\,\mathrm{M}_{\odot}$ from the FIRE project. Ne VIII
traces the volume-filling, virial-temperature gas in $\sim
10^{12}\,\mathrm{M}_{\odot}$ halos. In $\sim 10^{13}\,\mathrm{M}_{\odot}$ halos
the Ne VIII gas is clumpier, and biased towards the cooler part of the warm-hot
phase. We compare the simulations to observations by the CASBaH and CUBS
surveys. We show that when inferring halo masses from stellar masses to compare
simulated and observed halos, it is important to account for the scatter in the
stellar-mass-halo-mass relation, especially at $\,\mathrm{M}_{\star} \gtrsim
10^{10.5} \,\mathrm{M}_{\odot}$. Median Ne VIII columns in the fiducial FIRE-2
model are about as high as observed upper limits allow, while the simulations
analyzed do not reproduce the highest observed columns. This suggests that the
median Ne VIII profiles predicted by the simulations are consistent with
observations, but that the simulations may underpredict the scatter. We find
similar agreement with analytical models that assume a product of the halo gas
fraction and metallicity (relative to solar) $\sim 0.1$-$0.3$, indicating that
observations are consistent with plausible CGM temperatures, metallicities, and
gas masses. Variants of the FIRE simulations with a modified supernova feedback
model and/or AGN feedback included (as well as some other cosmological
simulations from the literature) more systematically underpredict Ne VIII
columns. The circumgalactic Ne VIII observations therefore provide valuable
constraints on simulations that otherwise predict realistic galaxy properties.
