Thunar needs to be installed to view the file>properties of images. I use Rox-filer and tend to uninstall thunar. If not run from the command line and thunar is not installed - properties fails silently. Run from the command line it give the following warning: (ristretto:6672): WARNING **: Failed to execute program /usr/bin/Thunar: Success At the very least add some sort of message about requiring Thunar. Better yet, make it so it doesn't required thunar to be installed to use.
Well, master currently does not require thunar to view properties. Currently, it does not show them at all.
To fix this, a file-properties dialog should be implemented in gtk or libxfce4ui, you don't want to write something that displays file-properties in 'yet another random way'. (tm)
I am developing a fix in the stephan/properties-dialog branch.
A properties-dialog is available, but it is barely usable. Setting the milestone to 0.5, the version to be released together with xfce 4.10
This is implemented in master, closing the bug.