Red foxes are found in much of the world. The United Kingdom, North America, Asia, and parts of Africa and the Middle East. They were introduced into Australia and they now flourish there.
These animals live in a wide variety of habitats. You can find them in the tundra, semi-arid deserts, metropolitan areas, and boreal forests.
Red foxes are omnivorous. They eat worms, insects, small rodents and rabbits. They eat berries, fruit, eggs, and seeds. Sometimes they will even eat small seals, fawns, turtles, frogs, snakes, and fish. They pretty much eat what is available where they live.
But back to size. Males are usually 3-6% larger than females. In the United Kingdom, the average size of a fox is 14 to 16 pounds. In Maryland, United States, the average is 9 pounds 6 ounces. Israel, Denmark, and Spain have noticed increases in sizes, while red foxes in France seem to be a little smaller.
It is believed that the available food is the culprit. Many of the foxes that seem to be getting larger have more access to more food. There are scraps from humans, of course, but the main source seems to be leftovers from farm animals. And as they get slightly larger they are able to feed on more farm animals. Areas of higher rainfall also seem to contribute to larger foxes.
What about genetics? While larger cubs grow into larger adults, so far the evidence seems to indicate that these cubs are simply more well-fed. At the same time maybe the potential for genetic growth is there and the food simply boosts it along.
I don't think you have too much to worry about yet unless you have a strong liking for red-hooded capes. Even so this will be another one of those things we will enjoy watching as time passes.