Good security designs increase convenience (eg ssh, touch id, single sign on).

The three goals of computer security are integrity, confidentiality and availability.

All three of those expand the usefulness of the system to the end user.

But the point here is not about integrity, confidentiality, or availability. It is about whether you trust Mozilla, and how much trustworthy they are.

A configuration where Mozilla cannot push remote updates is neither more secure nor less secure. Mozilla is often under fire for not allowing a privacy conscious, minimal trust use case.