This add-on for Mozilla Thunderbird with Lightning might be a one-hit wonder, but it provides a impressive service: it allows you bidirectional access to your Google Calendar in Lightning. To use it, you need to grab the XML link for your Google Calendar, under the Settings tab. Then go to new calendar in Lightning, choose Google Calendar, and paste in the XML URL. Voila: instant Google Calendar access, so that you can create, edit, and delete events in your Google Calendar from within Thunderbird. Likewise, changes made to your calendar on the Web are instantly reflected in Thunderbird.
There are few drawbacks in the add-on, mostly related to buggy support of more esoteric Google functions. For daily use, we encountered no problems and Google users should find this a must-have complement to Lightning.