Strange Safari Rendering Issues, And Low Performance On Other Browsers

I'm in the middle of development of a website, however I cannot work out what is causing this plethora of issues. In Safari on OS X (7.0.6 on 10.9.4), random elements will disappea

Solution 1:

I don't see any scrolling performance issue on chrome or firefox, but I noticed Safari rendering glitches.

When you force reflow, all your sections are displaying again. Try to add a backface-visibility:hidden; on your .section class.

Edit:

Your #background-area is fixed and doesn't have any z-index. Put it to z-index: -1; to keep it in the back.