This blog post is based on http://evolvisforge.blog.tarent.de/archives/124 .
Mozilla Firefox has a tentancy to create a ~/Desktop directory among
others (things like ~/Downloads). If you want to prevent this, you can
use the following commands:
mkdir -p -m0700 ~/.config
cat >~/.config/user-dirs.dirs <<EOF
XDG_DESKTOP_DIR="$HOME/"
XDG_DOCUMENTS_DIR="$HOME/"
XDG_DOWNLOAD_DIR="$HOME/"
XDG_MUSIC_DIR="$HOME/"
XDG_PICTURES_DIR="$HOME/"
XDG_PUBLICSHARE_DIR="$HOME/"
XDG_TEMPLATES_DIR="$HOME/"
XDG_VIDEOS_DIR="$HOME/"
EOF
Upon next start, Firefox (and other XDG-compliant applications) will
throw stuff into ~/ instead.