It is apparent from many of the ideas and discussions here that many users are unaware or untrained in basic functionality of the Firefox Browser such as configuring Search Engines, where files are saved, how extensions work, etc.
Clearly there is a point where hand-holding will hold back users more that empower them, so I do not recommend limiting or simplifying the current feature-set of Firefox, nor spamming the workflow with needless pop-ups and explanations. Instead, a "Tour" of Firefox should be an easily accessible and promoted option that will guide users through how the browser actually works and how to customize it. The option to use the tour should be presented as early as the first installation of Firefox, with clear instructions on how to access it next time should the user decline from a "First-Install" tour.
This would empower users to better understand Firefox without taking anything away from experienced users.