You may sometimes need to view or edit Thunderbird preference settings, which are not accessible through the normal user interface. You can use Thunderbird's Config Editor to do this.
To access the Config Editor, go to 
and select . Search for config and click on the button when it is displayed.
Clicking on the button in the display will show all hidden preferences in a tab called Advanced Preferences.
In the Config Editor, you can type a string in the field showing Search preference name to filter the list of preferences to only those that contain the specified string in their names.
To edit a boolean preference (true/false value), click on the Toggle button. For text preferences, double-clicking on the preference will enable in-place editing. Once the edit is complete, save your changes by clicking the checkmark
In rare cases, you may need to add a new preference. You shouldn't normally need to do this unless you are instructed to do so by documentation for Thunderbird or one of its add-ons.
To add a new preference:
- Type or paste the preference name into the search box.
- Select the appropriate preference type (number, string or boolean) from the offered options.
- Click on the Add to add the preference.
To delete a previously added preference, click the trash icon following the entry
Modifications to preferences happen immediately. However, some parts of Thunderbird or many add-ons only read their preferences on start-up, so it is good practice to restart Thunderbird after editing preferences for your changes to take effect. It is also important to know that when you restore a preference to its default value, Thunderbird does not store that preference in the preferences file. It is only non-default preferences that are stored.
