Firestone tires are bad for "blooming". Blooming is the leaching out of chemicals to slow down oxidation, as yamabob alluded to. I tried a couple of different brands on my Firestones, and now use Armorall Tire Foam. Makes the tires a beautiful black matte and lasts a long time, and no "blooming". They also have a product for shinny tires, Extreme Shine, however as I do not like the shinny "Hot Wheel" look, I have never tired it. Meguiar's gel was fairly good, a pain to apply, and you have to be careful of tire sling. Spray 303 is very good, but expensive and difficult to find in my area. And a few others, but the basic Armorall Tire Foam what I settled on. Nice stuff.