I'm running 18.04 and I have this error. However, I was able to get thumbnails working in Thunar. Ufraw is still segfaulting, but it creates the thumbnail first. So it seems it might be incidental and this bug is not causing the thumbnail issue.
The fix for me to get thumbnails was to run:
sudo update-mime-database
Then thunar -q, then restart Thunar.
I'm running 18.04 and I have this error. However, I was able to get thumbnails working in Thunar. Ufraw is still segfaulting, but it creates the thumbnail first. So it seems it might be incidental and this bug is not causing the thumbnail issue.
The fix for me to get thumbnails was to run:
sudo update- mime-database
Then thunar -q, then restart Thunar.