FWIW, "your ball joints need to be replaced" is an old-time auto scam. It works because it's safety-related, and the owner cannot directly check them without getting the car up in the air. My personal experience was that I bought a Contour, and was told (by Firestone, FWIW) it needed ball joints, so I had them done. Not six months later, THE SAME SHOP told me "you really need ball joints!"
(Boy, did they hem and haw when I showed my receipt!)
So, it's entirely possible that BOTH Firestone and NTB are pulling your leg. For obvious reasons, I'm underwhelmed by FS; NTB is a very "corporate" business, and I imagine employees derive bonuses by how much they "upsell" customers.
Take it to a NON-chain independent as a "referee." Let him know in advance you WON'T be using him for the work, so he won't have any incentive other than to give you his honest opinion.