Created attachment 2404 Patch that changes it from 36 to 32. THUNAR_ICON_SIZE_SMALL in thunar-enum-types.h is currently set to 36, a size which is not covered by standard icon themes. Consequently, the icons can appear blurred. It should be set instead to 32 to fix this.
This has already been fixed in 2147190c02c2ece7a924752a8d63bcf45e5568af.