Configuration Mania is a Firefox addon, can access more advanced features of your browser, gives you more Advanced (hidden) configurations from which to choose. How about a partial export? Prefs.js includes *everything*, and you may not want to clone your whole Firefox config. Youre more likely to have specific config options you wish to apply to others profiles.
The best way I can think of is exporting the desired settings to a user.js file. If a user.js file exists in the profile directory, it will be read, and setting in it will override those in prefs.js Since prefs.js is created and maintained by the browser, manual editing isnt recommended.

Requirements:
* Firefox

The license of this software is Free, you can free download and free use this browser plug-ins software.