Kaptinlin Themes Support

Hello!
I'm using Striking Wordpress Theme on www.interexsrbija.rs and I have one weird problem.
When I use Opera, IE10, Chrome on my Windows 7 site looks normal: http://i.imgur.com/m69aZ.png

But, when I visit site using Firefox 17.0.1 I get strange line below homepage slideshow and homepage looks like this (I've highlighted problem)
http://i.imgur.com/SMGbJ.png

I've tried to visit site from Windows XP and Ubuntu using Firefox and there is no problem. So this line is visible only using Firefox 17.0.1 on Windows 7 Professional. All other browsers and OS's which I tried are without problem. I've tried this from different computers.

I use only Simple Lightbox as plugin, and I did not change or edit any of Striking Theme files.
Wordpress is version 3.5 and Striking is on last version.

Please, help me with this problem.
Kind regards,
Draza