After selecting the show thumbnail bar option, ristretto freezes. After restarting it, it only shows a blank gtk window, with no menu or any content at all and freezes again. Can't be closed, only killed. When starting from a terminal doesn't show any errors. I observed this behavior in both my systems, openSUSE 11.4 and Archlinux, both 32bit and running Xfce 4.8. The ristretto version on openSUSE is 0.0.93 and 0.0.91, the version from Archlinux I don't know and can't check now.
Run this command as your regular user to get up and running again: xfconf-query -c ristretto -p /window/show-thumbnailbar -s false
Can you confirm if this problem still exists with git 5b93f4d94389e36053d2cbc4e7e98ca86e279892? (master branch)
The problem is gone with the latest git version.
Thank you, closing ticket :-)