With Lightning installed, you should see the Lightning Calendar icon at the top right, next to the Tasks icon.Click the calendar icon to open the Lightning Calendar tab.In the following window (Locate your calendar) you either have to provide your Google email address, log into your account, and grant Provider for Google Calendar permission to manage your calendars OR — if you have previously done that — you can pick an existing Google session.
And there you go, you have successfully integrated your Google Calendar Sync your Google Calendar with the Windows Calendar app wasn't always possible. Editing the calendar works both ways, meaning you can add and edit events via the website or in Thunderbird and they will automatically sync in either direction.
Since the Windows 10 Anniversary Update, you can even manage your Google, i Cloud, and Outlook calendars from the Taskbar. The Mozilla Wiki has a thorough page covering Provider of Google Calendar, including a section about bugs and limitations.
Check the calendars you want to add, click Next, wait for the confirmation that Your calendar has been created, and click Finish.
You should now see Lightning populated with your Google Calendar events.
There can be several reasons for the Sniffer to not process calendar requests.