Photon correlation spectroscopy in both polarized and depolarized geometries has been utilized to study density and orientation fluctuations in ZnCl2, ZnBr2, and their symmetric mixture in the metastable supercooled stare. The pure components display behavior intermediate between strong and fragile glasses reflected in the shape (L(log tau)) and dynamics (tau) of the relaxation function C(t), being similar for both density (C-rho(t)) and orientation (C-2(t)) correlation functions. In contrast to polymer blends, concentration fluctuations have no measurable broadening effect on the shape of C(t). Instead, L(log tau) becomes narrower with increasing temperature and affects differently C-rho(t) and C-2(t) for the zinc halide mixture. Despite local homogeneity in the thermodynamically ideal mixture, ZnBr2 with the higher glass transition temperature (T-g = 395 K) was found to dominate the primary alpha-relaxation in the symmetric binary mixture. In the framework of "two-fluid" models, the distribution and the temperature dependence of tau support rigid microheterogeneities on the order of 2 nm. The additional slow process, observed in fragile glasses so far, appears to affect also the anisotropic scattering from the pure components.