Firefox Preferences Editor is a CLI tool for batch configure Firefox about:config preferences. (Source Code)
Note:
Firefox will arrange prefs.js, so don't worry about duplicate entry.
Usage: ffprefs {preference name} {value}
e.g.
ffprefs browser.startup.homepage http://www.google.com
ffprefs browser.cache.disk.parent_directory r:\
v0.2 Update: Read %APPDATA% environment variable instead of %USERPROFILE%, support Windows 2000/XP/2003/Vista/2008/7
