Force Caja to create thumbnails

If in Caja has no thumbnails, check first that packages ffmpegthumbnailer and libffmpegthumbnailer4v5 are installed. If not, install and log out an in.

If that does not help, delete $HOME/.cache/thumbnails/fail folder.

rm -rf $HOME/.cache/thumbnails/fail

If that does not help, install Thunar and open folders using Thunar, so thumbnails are creating.