about:preferences#advanced in a recent version of Firefox presents a View Certificates button. Clicking that button brings up the Certificate Manager window. The Authorities tab in that window displays details of the certificate authorities (aka CAs) whose public certificates have been installed in the particular Firefox instance (or perhaps just the particular Firefox profile) currently in use.
This tab contains a table with two columns: Certificate Name and Security Device.
For each such CA, at least one entity exists in the table. At a glance, all the entities appear to be certificates, but I will continue to refer to them simply as "entities" here, as I have not (yet) checked them all. Each entity has an entry in both the Certificate Name and Security Device columns.
There appear to be only two valid values for entries in the Security Device column:
Builtin Object Token
Software Security Device
What is the (intended) difference between these two kinds of entity?