Preventing Firefox from creating Desktop directories

With a fresh firefox installation I found that it kept creating a ~/Desktop directory. But I found how to turn it off.

Edit ~/.config/user-dirs.dirs to

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/"

I had XDG_DESKTOP_DIR="$HOME/Desktop" which made a Desktop folder all the time.