Firefox add-ons come and go, you install them and uninstall them but the preferences you’ve set for them live on in about:config settings long after the add-ons are gone. For the simple add-on that performs harmless functions in your browser, the preferences may not be such a big deal but if you’ve used an extension to save sensitive information like login IDs or form data, you might want to wipe that information blank or you if you’re still using the extension and want to export your preferences to another system, the Preferences Cleaner is a Firefox extension that can removes preferences or save them in JSON format so that you can import them to another system.
To delete all preferences for an extension, open the Preferences Cleaner dialog box from Tools –> Preferences Cleaner and click the Loose Preferences button. A box listing preferences for installed and uninstalled extension will open. Select the extension that you want to remove preferences of; select all preferences listed for that extension and click Delete Choosed Preferences. You can select a single preference and click Delete Choosed Preference to remove a single one. To export a preference for an extension you’ve uninstalled, follow the above procedure and click Preferences export instead of Delete Choosed Preferences and the preference will be saved to a JSON file.
To export preferences for installed extensions, open the Preferences Cleaner dialog box and select Preferences Export and drag & drop the extension from the list to the new dialog box. You can remove a preference by clicking Remove or save them to JSON forma by clicking OK.
The extension gives you a complete list of all preferences for each installed extension, and lets you export or remove them collectively or individually. It also makes it easier to search for preferences installed with an extension. You can copy the preference name and modify it in about:config.