Keywords: Google Calendar, Mozilla Sunbird, Provider for Google Calendar
Sunbird have two network calendar built-in providers. One is iCalendar(ICS), another is CalDAV. You can use ICS to subscribe the google calendar, but it is not allowed to update into google Calendar by this way.
Privider for google calendar is an extension of Sunbird and ThunderBird. It will provide another format to support sync google calendar.
Pay attention to the extension and sunbird version. If they are not compatible, there is not Google Calendar format in the create new calendar wizard of Sunbird.
But, at present Provider for Google Calendar 0.31 is out of work in sunbird 0.7