After I tried to enable show thumbnail in ristretto (image viewer), the application freeze. Whatever image I open with ristretto, all will freeze. To solve this, remove ~/.config/xfce4/xfconf/xfce-perchannel-xml/ristretto.xml, logout, and login. The application will not freeze anymore. But I don’t try to enable the thumbnail after this.
Arch Linux Ristretto show thumbnail freeze problem