Config Editor

Thunderbird's Config Editor may be used to view or edit Thunderbird preference settings, which are not accessible through the normal user interface. Modifications made are unsupported and used are at your own risk.

To access the Config Editor:

• Click ≡ > Settings > General
• Scroll down to the bottom and click Config Editor...

Clicking on the Show All 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.

Note: Preferences that have been changed from their default values are shown in bold. There is a revert arrow on the end of the entry to change the setting to the default value

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 should not normally need to do this unless you are instructed to do so by Thunderbird documentation or one of its add-ons.

To add a new preference:

1. Type or paste the preference name into the search box.
2. Select the appropriate preference type (number, string or boolean) from the offered options.
3. Click on the Add to add the preference.

To delete a previously added preference, click the trash icon following the entry

Changes to preferences are stored 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. Only non-default preferences are stored in the preferences file.