Guide: Using GeneralSync with Mozilla Thunderbird

This guide describes the GeneralSync integration provided by the official Thunderbird add-on. It is divided into the following feature-specific sections:

  1. Installation: enabling GeneralSync features in Thunderbird
  2. Calendars: viewing and editing events
  3. Address books: viewing and editing contacts

Note that this document is intended as reference providing some background information on the GeneralSync integration; it is not required to read through this document in order to use GeneralSync. If you are not yet familiar with Mozilla Thunderbird, you might want to check out the official support resources provided by Mozilla as well. Thunderbird features unaltered by the GeneralSync integration will not be covered in this guide.


While starting GeneralSync for PC for the first time, the first-run setup installs the add-on by default. On the next start of Thunderbird, you will get prompted to confirm the installation:

Screenshot: add-in installation confirmation

Check the option Allow this installation, click continue and confirm the required restart to enable GeneralSync features.

If you did not choose to install the add-on during the first-run setup, or switched your Thunderbird profile, you can also install the add-on manually:

  1. Download the most recent version of the add-on (license agreement)
  2. Open Thunderbird's add-on manager (Menu|Add-ons, or Tools|Add-ons on the classical menu bar).
  3. Select the Extensions-Category (puzzle-icon on the left).
  4. Above the list of extensions, click on the gear button, and select Install Add-on From File.... Select the file downloaded in the first step.
  5. Confirm the installation.


If you have the Lightning extension enabled (default since Thunderbird 38), Thunderbird provides calendar features. This section describes how to use Calendars managed by GeneralSync. If Lightning is not enabled, you cannot use Calendars with Thunderbird.

Adding a GeneralSync calendar to Thunderbird

Calendars available through GeneralSync are automatically added to Thunderbird. You can also create new GeneralSync calendars directly from Thunderbird by right-clicking on the list of calendars in the calendar tab:

Screenshot: calendar tab with context menu of calendar list

Then, select the option New Calendar.... The new calendar dialog will open:

Screenshot: new calendar dialog, type page

Choose the option Decentralized via GeneralSync and continue to specify the details for the new calendar:

Screenshot: new calendar dialog, config page

Similar to any other calendar used in Thunderbird, you can specify a name, color, and whether or not you wish to be notified on alarms within the calendar you're adding. The settings on this page are not synced by GeneralSync. It is thus possible to assign different names in Thunderbird and on GeneralSync, simply by renaming the calendar in the GeneralSync dashboard later on.

Setting the correct email address is essential for event invitations: Thunderbird will use the given address to send event invitations and to find a suitable calendar for incoming event invitations.

Once you confirmed your configuration, the calendar can be used in Thunderbird:

Screenshot: new calendar dialog, finish page

Migrating to GeneralSync

If you wish to use an existing calendar with GeneralSync, perform the following steps:

  1. In the calendar tab, right-click the existing calendar, and choose Export Calendar....
  2. Save the calendar to a location of your choice.
  3. Add a new GeneralSync calendar, as explained above
  4. In the menu, choose Events and Tasks|Import Calendar..., then select the calendar file saved in the second step and choose the GeneralSync calendar as target.
  5. Verify that all events were transferred correctly. Afterwards, you may remove the original calendar from Thunderbird. If you do not want to keep it as a backup, you can also remove the file created in step 2.

Event version information

On calendars linked with GeneralSync, you can view version information on each event in the event editing dialog:

Screenshot: edit event dialog with version information, top part

The displayed information consists of a timestamp of the last change, and the device issuing the change. If the device issuing the change is not paired or otherwise has no known name, a technical device ID is displayed instead.

Resolving Conflicts

If the same event is changed on multiple devices, GeneralSync cannot automatically determine which change should be kept. The event will thus be in a conflict state, and can't be displayed in the calendar.

Thunderbird notifies you of existing conflicts with a warning sign in the bottom left corner of the calendar tab:

Screenshot: calendar tab with conflict warning

You can view conflicting versions by clicking on Resolve conflicts...:

Screenshot: conflict dialog with event

Select the version you wish to keep, and click Resolve to save your selection. Your selection will then be synced to other devices automatically.

If you do not wish to select a version right now, you can use the Skip button to go to the next conflict, if any. Once all conflicts were resolved or skipped, the dialog finishes:

Screenshot: conflict dialog, finish page

Address books

This section describes how to use address books managed by GeneralSync as regular address books in Thunderbird.

Adding a GeneralSync address book to Thunderbird

Address books available through GeneralSync are automatically added to Thunderbird. You can also create new GeneralSync address books directly from Thunderbird through the address book window (accessible through a toolbar button in the main window):

Screenshot: adding a new address book

Choose File|New|GeneralSync Address Book. A dialog will ask you for the address books name; once you confirmed the name the new address book is ready to be used. Just like with calendars, you can rename the address book in the GeneralSync dashboard later, without changing its name in Thunderbird.

Migrating to GeneralSync

You can drag and drop existing contacts into GeneralSync address books. Thus, the easiest way to move contacts from existing address books to GeneralSync is to select them (Ctrl+A to select all entries) and drag them onto a newly created address book.

Differences to regular Thunderbird contacts

Screenshot: Fields for postal adresses

For contacts stored in a GeneralSync address book there are minor differences to regular contacts:

Resolving Conflicts

If the same contact is changed on multiple devices, GeneralSync cannot automatically determine which change should be kept. The contact will thus be in a conflict state, and can't be displayed in the address book.

If any of your address books contain conflicting contacts, a warning is shown below the list of address books:

Screenshot: address book window with conflicts

Conflicts are also displayed in the properties of affected address books. Click on Resolve conflicts... to open the conflict resolution UI:

Screenshot: conflict resolution for contact

You can then select the change you wish to keep and click Resolve, or click skip to immediately skip to the next conflict without resolving. After resolving a conflict, its resolution is synced back to all other devices. You thus do not need to resolve the same conflict twice.

Thank you for using GeneralSync!

Feel free to contact us if you have further questions or suggestions regarding this guide or GeneralSync itself.