Firefox v57 notice:
OPIE is considered a 'legacy' extension and will no longer work with Firefox v57 and above. OPIE cannot be written with the WebExtensions platform that Mozilla has adopted for all extensions. OPIE will still be maintained, but only for Firefox clones (like Pale Moon).
OPIE (Ordered Preference Import/Export) is a Firefox extension that allows you to import and export your installed extension preferences. This is useful when installing extensions in a new profile, or synchronizing multiple Firefox installations.
Once installed, OPIE is available from the Firefox Tools menu. An icon can be placed on the toolbar via (right-click on toolbar) > Customize...
OPIE is a companion to FEBE and CLEO.
OPIE2 1.0 is available now on AMO. It is an advanced version of OPIE with the ability to more finely tune which preferences are exported.