I know this is a troll account, but in case anyone wants a serious answer: the AUR is a user based repository for people to download software and programs. It's not officially run by Arch, but has a team of folks who oversee the packages to try to maintain order. In there, people can upload just about anything. So the issue of "this program isn't on XYZ distro" is not an issue on Arch. Debian is known as one of the most stable distros a user can find, but it suffers from programs which are often times VERY VERY old, and at times, a lack of modern software that is not maintained in the official repositories. Baseline Firefox is a perfect example. Debian maintains Firefox ESR which is basically a long term support release version of firefox, that CRAWLS along in updates and new features. By adding the DUR, users now have the option to download software that isn't even available in the testing or unstable repos, which still (in theory) maintaining the overall stability that Debian affords.