Why in the world would you even consider marking comments or attachments as private on bugzilla?
The purpose of a bug report is to provide as much information as possible and reasonable for the maintainers to find and fix bugs. As I understand it using ‘private’ would limit the number of eyes that may be able to read the posted info and thus would make triage and finding a solution much harder.
You should never post personally identifying information on bugzilla anyway.