  We present an optical variability study of 44 newly identified blazar
candidates behind the Magellanic Clouds, including 27 flat spectrum radio
quasars (FSRQs) and 17 BL Lacertae objects (BL Lacs). All objects in the sample
possess high photometric accuracy and irregularly sampled optical light curves
(LCs) in I filter from the long-term monitoring conducted by the Optical
Gravitational Lensing Experiment. We investigated the variability properties to
look for blazar-like characteristics and to analyze the long-term behaviour. We
analyzed the LCs with the Lomb-Scargle periodogram to construct power spectral
densities (PSDs), found breaks for several objects, and linked them with
accretion disk properties. In this way we constrained the black hole (BH)
masses of 18 FSRQs to lie within the range $8.18\leq\log (M_{\rm
BH}/M_\odot)\leq 10.84$, assuming a wide range of possible BH spins. By
estimating the bolometric luminosities, we applied the fundamental plane of
active galactic nuclei variability as an independent estimate, resulting in
$8.4\leq\log (M_{\rm BH}/M_\odot)\leq 9.6$, with a mean error of 0.3. Many of
the objects have very steep PSDs, with high frequency spectral index in the
range $3-7$. An alternative attempt to classify the LCs was made using the
Hurst exponent, $H$, and the $\mathcal{A}-\mathcal{T}$ plane. Two FSRQs and
four BL Lacs yielded $H>0.5$, indicating presence of long-term memory in the
underlying process governing the variability. Additionally, two FSRQs with
exceptional PSDs, stand out also in the $\mathcal{A}-\mathcal{T}$ plane.
