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Right-click below the 'Calendar' heading.In Thunderbird, find the Calendar area in the left-hand sidebar.
Add Google Calendar(s) to Thunderbird client. The Google Calendar Private Address in iCal (.ics) format will be a URL of this form. Find your Google Calendar Private Address in iCal format. Toggle to the calender by clicking the 'Calendar' icon. In Thunderbird's lower-left corner, new icons let you toggle among 'Mail, 'Calendar', and 'Tasks'. Thunderbird -> Tools -> Add-ons -> Install This extension allows Sunbird and Lightning to read and write events to a Google Calendar. Download the Thunderbird Provider for Google Calendar Add-On. This extension allows you to manage your daily schedule (events and tasks) directly within Thunderbird. Download the Thunderbird Lightning Add-On. You do need - at the very least - Thunderbird 24 and Lighting 2.6, as they support the new option.You can turn your Thunderbird e-mail client into a Personal Information Manager (PIM) by integrating your Google Calendar(s) into Thunderbird. Update: Google changed the authentication method of CalDAV on September 16.
Lastly, you need a Google account with Google Calendar enabled as a service.
The developers however have stated that the next version of Lightning will again support previous versions of Thunderbird as well. 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. Probably better than that is the integration of Google Calendar information into the Lightning add-on as it integrates better with Thunderbird. In 2010 I reviewed the Thunderbird add-on Google Calendar Tab which integrates the service into Thunderbird by opening the Google Calendar web page in the email client. Using Lightning is not the only way of integrating Google Calendar in Thunderbird. Both the Thunderbird desktop email client and the Lightning calendar add-on have been recently updated.