I can't take credit for this because I was told of its existence by Simon Fraser, a Camino (previously called Chimera) developer. There are hidden preferences in Camino that can be set via a special user.js preferences file. The file needs to be created in this path: ~/Library -> Application Support -> Chimera -> Profiles -> default -> random.slt, where random.slt is uniquely named for each user (for security reasons).
The user.js file can contain different settings for preference variables (thus over-riding prefs.js settings), as well as some other "hidden" settings. In my case, I wanted to recover the ability to download files with a save window that allows me to select a different directory each time. So I made a file called user.js in the noted directory, and put the following single line in it:
user_pref("browser.download.autoDownload", false);
As far as I know, this one is not documented anywhere.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2003040321350058