It doesn’t necessarily mean it, but the context here is pretty obvious. Firefox has long been privacy friendly.

However, like others pointed out, this feature is useful in numerous use cases beyond just privacy. E.g. one of the systems I manage at work is a stand alone network, i.e. not connected to any external network whatsoever. I’ve had instances where having this feature would’ve been convenient. Then you have scenarios where you’re offline on a plane or an Internet outage or whatever. Your browser can open all kinds of document types, not just HTML (e.g. text files, PDF files, etc.).