Mozilla Firefox allows you to add new features and functions through the use of extensions. There are thousands and thousands of freely available extensions that you can install in Firefox. When you install a new extension in Firefox, that extension sets up its own preferences in the prefs.js file which is located in the Firefox profile folder. But even after you have removed that extension from Firefox, some of the preferences are left behind and make this preferences file larger with time. A larger preferences file can increase the load time of the Firefox web browser and may also impact its overall performance. But now you can use the Clean Uninstall extension for Firefox to get rid of the left behind preference entries from Firefox.
The Clean Uninstall extension makes it very easy for you to remove the preferences entries made by various extensions by allowing you to remove these entries at the time you choose to remove those extensions. So after you have installed the Clean Uninstall extension, you can try removing any other extension by going to the about:addons screen. As soon as you click on the Remove button for any extension, Clean Uninstall will show you a list of preferences created by that extension. You have to options to selectively remove them, remove them all or leave them all. After this, the removal of that extension takes place in the usual manner.
If you have already uninstall some extensions, then Clean Uninstall can help you clean up the entries left-over by them. For this, you have to open the Clean Uninstall options from about:addons screen. There you can find a button Open Cleaner clicking on which a list of all entries created by all the extensions (past and present) will be displayed.
In this list all the extensions that are currently installed are shown in light grey color and cannot be selected. The extensions that were installed in Firefox in the past but were later uninstalled can be selected for removal. You can see how many entries each of the extensions have created in the prefs.js file. You can select the extensions that you know that you have removed and proceed with their removal.
Conclusion: Clean Uninstall can remove the orphan and obsolete entries left behind by the extensions you have uninstalled long ago. It can help you keep your Firefox preferences file small and gunk free.
You can download the Clean Uninstall extension for Firefox from https://addons.mozilla.org/en-US/firefox/addon/clean-uninstall/.