Mluzan, did you ever hear of Leaf Miners? This guess is probably a long shot, but check it out..I hope anyway..
Is the plant out or indoors? Though soil shouldn't stay constantly moist, when you do water, water entire rootball. Ficus thrive in direct sun, but need to be taken out gradually..
One other this is fertilizer..Have you fed it lately? You're not overfeeding??? Toni

Most species of Ficus exhibit cupping/curling of leaves when grown in very bright light (and tropical sun certainly qualifies as bright).

Al

Are they folding up lengthwise along the center so that they look like a pea pod? Open up a folded leaf and check inside for thrips. There is a type of thrip (I forget the name) that has become a real problem in ficus from Florida. I had some on some indoor ficus but they seemed to affect the new growth, not the older leaves.