I'm not this if this is a CSS problem, but I'm guessing it is.
If I set the leightbox display status to 'block' manually (so the website loads with the leightbox popped up already) there is no problem.
Since only the jump menus disappear I'm quite confused what could be the problem. Is there anyone who might know what's causing this? If neccessary, I can post some more code.
border: 1em solid #333;