Firefox is trying to set a world record for downloads in a day. The Firefox page includes a nice map showing where the downloads are occurring. So far, the top 5 countries for downloads, in order, are 1) the U.S., 2) Germany, 3) Spain, 4) United Kingdom, 5) and France (barely over Brazil and Canada).
Addendum: As of June 19 at 1:48 cst, the top 5 countries are still the same, with the United Kindgom taking 3rd place. The country with the fewest downloads is North Korea with 0. The country with the fewest downloads with a minimum of 1 is Guinea-Bissau with 2. Other interesting spots are Iraq with 498, Iran with 269,390, Cuba with 2,057, Myanmar with 742, and Greenland with 192.