CalDav fixed! Rated 5 out of 5 stars
Tbird 2.4.11 + Lightning 2.6.3 - Google CalDav works again! Lightning is once again an awesome, essential add-on for Tbird.
Since Google revised CalDav, in September, we've been waiting for the fixes. Overdue, but working great now. Yay!
The instructions for the new Google CalDav connection are here: https://blog.mozilla.org/calendar/2013/09/google-is-changing-the-location-url-of-their-caldav-calendars/