  We study different maximum principles for non-local non-linear operators with
non-standard growth that arise naturally in the context of fractional
Orlicz-Sobolev spaces and whose most notable representative is the fractional
$g-$Laplacian: \[
(-\Delta_g)^su(x):=\textrm{p.v.}\int_{\mathbb{R}^n}g\left(\frac{u(x)-u(y)}{|x-y|^s}\right)\frac{dy}{|x-y|^{n+s}},
\] being $g$ the derivative of a Young function.
  We further derive qualitative properties of solutions such as a Liouville
type theorem and symmetry results and present several possible extensions and
some interesting open questions. These are the first results of this type
proved in this setting.
