Menu layout not rendering properly in Firefox

Hi everyone, I was trying to build a new site (studio19designgroup.com) with the theme Klasik Framework. The menu is fine in Safari, but when I checked it in Firefox, it is not displayed properly. I tried to change the font size of the menu before, but didn’t succeed (I am completely a layman in CSS…). So I thought probably I messed up with some codings. Then I changed all the style.css to the original one that came within the theme folder. But the problem still exists.

Could anyone help me with that? Many thanks!!!