I think your problem lies here
<div class="slider-wrapper theme-default"> <div id="slider" class="nivoSlider" style="width:414px !important; height:165px !important;"> <img src="images/ElBan2.1.png" alt="DJELLERY GRAND OPENING" title=" DJELLERY GRAND OPENING " width="830" height="277" />
First you tell the slider to be 165px high, which Chrome obeys.
Then you have your pictures with a height of 277, which Firefox uses

So changing the 165xp should solve the problem