When you load the frontpage, the first slide is not shown.
You can see all the slides fade to left then some seconds of background and then the second slide come from right.

I checked on cslider demo site (http://tympanus.net/Development/ParallaxContentSlider/)
and I fixed it removing da-slide-toleft class in /moodle/theme/essential/layout/frontpage.php lines 204-268

For example:
with da-slide-toleft
http://2013.imoot.org/

my fixed site
https://amianto.dir.unipmn.it/

HTH