Dust is promoter of devitrification. You should do the most you can to keep your kiln free of dust.
Dust can come from the kiln lining materials. Regular gentle vacuuming of the kiln surfaces will help prevent particles from falling on to you work or other surfaces in the kiln.
It can come from the separators you put in the kiln. I often see pictures of used fibre paper at the side, or under, the kiln shelf. This should be cleaned out after each use to provide clean firing conditions.
The main reason for this obsessive cleaning is that dust particles within the kiln will be disturbed by the air movement involved in closing or opening the kiln lid or door. There also is air circulation within the kiln during the heating and cooling phases, although it is not as much as when opening the door/lid. These disturbed dust particles will settle on the glass and defeat your cleaning of the glass.