The eCleaner add-on can be used to clear all these breadcrumbs left by the previously installed extensions.
To see the list that is about to be deleted, go to the add-ons` list and locate eCleaner. Open his Preferences window and you will be shown a list with saved preferences, and their corresponding number of stored values.
Select the extensions which you no longer have installed and click the "Clear Selected" button.
Note: The eCleaner add-on is cross-platform and it works on Mac OS X, Windows and Linux.
