I want to enable thumbnails for camera raw files (nikon .nef) in the file manager. I added a .thumbnailer file in /usr/share/thumbnailers and in the Exec= line I've tried gdk-pixbuf-thumbnailer and ufraw-batch (which I installed), but with no result. Apparently gdk-pixbuf-2.0 is installed but it's not present in /usr/bin. How do I do this properly?