I think I have tried every permutation of configuration to synchronise Lightning with Google calendar. I have Thunderbird 31.1.2 and Lightning 3.3.1 The GDATA provider has the well documented issue of either re-mailing all meeting attendees, or not sending out invitations to meetings, so this doesn't really work for me. I have succeeded in seeing my Google calendar by using the iCalendar(ICS) option, but whenever I add a new calendar event in Lightning I get a "An error occurred when writing to the calendar 'My Name'! Error Code : MODIFICATION_FAILED When I try using CalDAV I don't see the events in my Google calendar in the resulting calendar in Lightning. I'm not sure I have the right 'Location' parameter, I have multiple Google calendars, the details available on the various web forums are not very explicit about how to get the location when using multiple Google calendars. Finally the Post on the Mozilla support forum states that I should use the Google Calendar option, which is not present! I am sure this is possible, any help would be appreciated. I have now turned on full logging and see the error: [JavaScript Error: "[calCachedCalendar] replay action failed: null, uri=https://www.google.com/calendar/dav/{myusername}%40gmail.com/events, result=2147500037, op=[xpconnect wrapped calIOperation]"] I think I have solved this one already. Deatails of the correct CalDAV locations can be found here: https://blog.mozilla.org/calendar/2013/09/google-is-changing-the-location-url-of-their-caldav-calendars/ and here: https://developers.google.com/google-apps/calendar/caldav/v2/guide#connecting_to_googles_caldav_server It would be useful to update the Mozilla documentation accordingly. Can I help do that?