I have the same problem as described in this thread: https://support.mozilla.org/en-US/questions/1230294 I have installed the Provider for Google Calendar add-on and done the following steps: 1. Right-click -> Add calendar 2. Chose On the Network 3. Chose Google Calendar 4. Entered my gmail address 5. Logged in to Google account in the popup 6. Approved permission for Provider for Google Calendar Then I get no further as the list of calendars to subscribe to is empty (screen shot attached). The discussion in the archived question mentioned old calendars that needed deleting but I don't have such. I can add that I also cannot connect Thunderbird to Gmail using OAuth authentication. So there might a general problem communicating with Google.