  We study the Majorana surface states of higher-spin topological
superconductors (TSCs) that could be realized in ultracold atomic systems or
doped semimetals with spin-orbit coupling. As a paradigmatic example, we
consider a model with p-wave pairing of spin-3/2 fermions that generalizes
${}^3\text{He-}B$. This model has coexisting linear and cubic dispersing
Majorana surface bands. We show that these are unstable to interactions, which
can generate a spontaneous surface thermal quantum Hall effect (TQHE). By
contrast, nonmagnetic quenched disorder induces a surface conformal field
theory (CFT) that is stable against weak interactions: topological protection
is enhanced by disorder. Gapless surface states of higher-spin TSCs could
therefore be robustly realized in solid state systems, where disorder is
inevitable. The surface CFT is characterized by universal signatures that
depend only on the bulk topological winding number, and include power-law
scaling of the density of states, a universal multifractal spectrum of local
density of states fluctuations, and a quantized ratio of the longitudinal
thermal conductivity $\kappa_{xx}$ divided by temperature $T$. By contrast,
$\kappa_{xx}/T$ for the clean surface without TQHE order would diverge as $T
\rightarrow 0$. Since disorder stabilizes the conducting Majorana surface fluid
and quantizes thermal transport, our results suggest a close analogy between
bulk TSCs and the integer quantum Hall effect.
