96 I think, in any infinite fox scenario, oxygen turning into carbon dioxide would be the least of your worries. If enough foxes got piled up in one place, they'd turn into a soup of (mostly) carbon, hydrogen, oxygen, and nitrogen. As the fox pile reached the scale of planets, their combined gravity would form them into a ball held up by a combination of thermal pressure (as the material in the middle of the ball is compressed adiabatically and heats up) and electron degeneracy pressure. At some point, the temperature in the core might reach high enough pressure and temperature that the hydrogen in what used to be water molecules, carbohydrates, and proteins would start to fuse into helium- or maybe not; I don't know how much the abundance of heavier elements would affect that. In any case, the fox ball would most likely start to act like a CO white dwarf (although with more nitrogen, hydrogen, and helium than a typical CO dwarf has), and, when its mass reaches about 1.44 times the mass of our Sun, would become so massive that the electron degeneracy pressure gives out. The core of the ball would collapse, causing the carbon and oxygen to rapidly start fusing into silicon, magnesium, sulfur, maybe a few other elements that I don't remember off the top of my head, and ultimately iron and nickel. This rapidly increases the temperature in the core, causing a massive runaway episode of nuclear fusion that ultimately blows the entire ball to smithereens, sending large amounts of hot gas, dust, and bits of short-lived foxes into space.
Centuries later, alien astronomers in a distant galaxy observe what we would call a Type 1A supernova. They observe its apparent brightness and the rate at which the light coming from it trails off, and in doing so obtain an estimate of the distance between their homeworld and ours. They note some odd-looking lines in the supernova's spectrum, and wonder what could have caused them.