The fully kinetic theory of low-frequency electromagnetic modes in high-¿ plasma is developed accounting for finite ion-Larmor radius effects (FLR) in non-Maxwellian space plasmas. The most general linear mirror mode dispersion relation is derived for arbitrary velocity distributions in the fully kinetic limit. Closer inspection shows that this dispersion relation describes two different instabilities. The first one corresponds to the classical mirror instability on the slow mode branch including FLR effects. Its growth rate attains a maximum at wavelengths the order of the ion gyroradius. Furthermore, if the plasma is mirror stable, i.e., when the condition for the mirror instability is not satisfied, another instability arises in the presence of a halo on the tail of the ion distribution. We term this new instability halo instability. It grows complementary to the mirror instability on the fast mode branch. It arises under conditions when the ratio of halo and thermal velocities exceeds some well-defined critical value.