OpenRaster is a file format proposed for the common exchange of layered images between raster graphics editors.
I created a simple python script (adapting this one, written by David Revoy) that creates the file thumbnail, then all it's needed is the thumbnailer to call the script. Open a terminal window and run:
wget -q http://goo.gl/cbXjm -O- | sudo tee /usr/local/bin/openraster_thumbnailer.py wget -q http://goo.gl/nlODH -O- | sudo tee /usr/share/thumbnailers/openraster.thumbnailer sudo chmod +x /usr/local/bin/openraster_thumbnailer.py
ReferencesOpenRaster at Wikipedia
Krita kra file thumbnailer for Gnome,Nautilus (Linux)