Probably better than that is the integration of Google Calendar information into the Lightning add-on as it integrates better with Thunderbird. The requirements are the following: You need Thunderbird 8 or later at the moment as Lightning is only compatible with that version of the email client currently. The developers however have stated that the next version of Lightning will again support previous versions of Thunderbird as well. Lastly, you need a Google account with Google Calendar enabled as a service.

Installing Lightning

Install Lightning in Thunderbird by dragging and dropping the downloaded add-on file into the program window. You can alternatively click on Tools > Add-ons to open the program’s add-on manager. Click the small options icon next to the search and select Install Add-on from File. Locate the Lightning add-on on your computer and select it to install it in the email client.

Restart Thunderbird after you have installed the calendar add-on.

Setting up Google Calendar

Go to the Google Calendar website and log into your Google account. Click on the options icon in the upper right corner of the screen next to the profile picture and select Calendar settings from the menu there.

Switch to the Calendars tab under Calendar Settings and locate the calendar that you want to sync with Thunderbird. Click on that Calendar and scroll down until you Calendar Address and the Calendar ID listed there.

Syncing Google Calendar with Thunderbird

Click on File > New > Calendar to create a new calendar. In the next menu select On the Network from the available options and click Next.

Select CalDAV from the available options and paste in the following url:

https://www.google.com/calendar/dav/[Calendar-ID]/events

with Calendar ID being the ID listed on the Google Calendar page.

You are then asked to enter a name, color, alarms and an email address for the calendar.

If everything has been done correctly the Google login credentials need to be entered on the next page. Once done the new calendar will be displayed in the Lightning calendar in Thunderbird.