Running ristretto gives this message: "The thumbnailer-service can not be reached, for this reason, the thumbnails can not be created. Install Tumbler or another thumbnailing daemon to resolve this issue. [ ] Do not show this message again <OK>"
Created attachment 311081 [details] suggested patch
nah, I explicitely asked upstream to show the warning dialog so I don't have to add the depend in the ebuild, http://bugzilla.xfce.org/show_bug.cgi?id=8176