Firefly Render Settings
After reading countless tutorials and using a range of other artists's settings, I realized that I still had no idea what the various Firefly options actually did. What I wanted most was a side-by-side comparison of exactly how each setting affects a finished render, and I couldn't find one anywhere, at least not in the kind of detail that I wanted. Since everyone's ideal settings are likely to be slightly different, I'm not going to suggest that you copy mine. What I am going to do is provide the detailed comparison that I wish I'd had.
Start With a "Control" Setting
To run my battery of tests, I threw together a very basic scene and started with lower settings: