The animal on the cover of Programming Firefox is a red fox (Vulpes vulpes, Vulpes fulva). Found throughout Canada, Alaska, most of the contiguous United States, Europe, Asia, and parts of northern Africa, the red fox is the most widely distributed wild carnivore in the world. Its habitat includes forests, tundras, prairies, farmlands, and increasingly, suburban areas. Red foxes are identified by their reddish-brown coats, white-tipped tails, and black ears and legs. Although American red foxes are typically smaller than their European counterparts, the average size of the red fox is 36-42 inches long (including its 15-inch tail) and 16 inches tall, weighing approximately 15 pounds.

Red foxes are solitary and do not form packs like wolves. For most of the year, they sleep concealed in high grasses or thickets. The exception is breeding season, during which a fox pair establishes a den, often taking over one created by rabbits or marmots. Foxes may dig larger dens in the winter, or during birth and rearing of their pups. The same den is often used over a number of generations. With tunnels connecting the main den to other nesting sites, the animals generally remain in the same home range for life.

Red foxes feed on insects, earthworms, small birds and mammals, eggs, carrion, and vegetable matter. Although they have a reputation for raiding chicken coops, they're often beneficial to farmers because they keep the rodent population low. They have a distinctive method for catching mice: they stand perfectly still, listening and watching intently, then leap high, bringing their forelimbs straight down to pin the mouse to the ground. However, because of their small size, red foxes are not only predator, but also prey: they're hunted by larger mammals such as wolves and bobcats, and pups are often killed by birds of prey. Humans, who kill red foxes for their fur and for sport, are the red fox's biggest predators. In 2005, foxhunting-a popular sport in Europe since the 14th century-was banned in Great Britain, and most fox species continue to flourish.

The cover image is from the Dover Pictorial Archive. The cover font is Adobe ITC Garamond. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont's TheSans Mono Condensed.