Ficus lyrata, commonly called fiddle leaf fig, grows more than 30 feet tall in its native habitat and grows outdoors in U.S. Department of Agriculture plant hardiness zones 10 through 11, or as a houseplant. Fiddle leaf figs are susceptible to a few pests or diseases. Brown leaves that fall off the plant are typically the result of a problem with its care.
Water Problems
Fiddle leaf figs are tropical rain forest natives, accustomed to high humidity, consistent temperatures and well-draining, peaty soil. When the plants receive too little water, new foliage browns and eventually falls off. Conversely, when plants are over-watered -- or heavy soil becomes waterlogged -- damage begins at the base of the plant and the oldest leaves turn brown and drop. Allow over-watered figs to dry thoroughly. Fiddle leaf figs should be allowed to dry out between waterings and then watered deeply until water runs out the bottom of the container.
Drafts
Fiddle leaf figs, like other tropical plants, crave humid conditions because life on the rain forest floor is still and warm. When cold, dry winter drafts blow through doors and poorly sealed windows, they leaves may dry and drop on the side of the plant that feels the draft. Radiators or air conditioner outlets may also desiccate leaves, so don't place fiddle leaf figs near them. Unlike weeping figs (Ficus benjamina), which might drop bunches of leaves after exposure to a draft, fiddle leaf figs lose leaves one at a time.
Soil and Roots
Crowded roots and too much nitrogen in the soil can cause leaves to turn brown and drop. Overcrowded roots cannot use water or nutrients efficiently. Too much nitrogen fertilizer burns leaves from the inside, resulting in browning and dropping. Repot plants into the next size larger pot when roots start growing through drainage holes. When you repot, prune off roots that encircle the root ball. Use a slow-release fertilizer to limit nitrogen release during the growing season. In winter, when active growth slows, do not fertilize your fiddle leaf fig.
Insects
Insects that feed on the carbohydrates and nutrients that circulate through leaves are not major pests of fiddle leaf figs, but infestations can cause leaves to yellow, then brown and drop. This is more common with plants that have been outside for a while. Inspect your fiddle leaf fig carefully before bringing them inside. A wipe down of all leaf surfaces with a solution of 1/2 teaspoon of plain dishwashing detergent in 1 gallon of water, followed by a tepid shower in the bathroom, may discourage spider mites, aphids, whiteflies and thrips planning on a winter migration to indoor warmth.
Diseases
Root rot due to over-watering causes browning, but typically, diseases begin with spots or browning along the margins of the leaves. Once root rot progresses enough to be noticeable, the plant might be too far gone to save. Bacterial leaf spots and anthracnose, a fungal disease, may also be responsible for spotting, but if entire leaves begin browning and dropping on a fiddle leaf fig, it may be best to replace the plant.
Jill, that plant is gorgeous! Don't think we have Seasol here, but if not, I'll find something similar when I repot it. It doesn't look good; yesterday I just brushed against it, and a leaf fell off....tho, it is getting more light now, so hoping it comes back. 
