Puntuado con 4 de 5 estrellas
Contrary to Anon.426068's assertion, this plugin works perfectly with the current release version of Thunderbird. It's only the latest BETA version that it isn't yet compatible with. Only beta users will be impacted, which is what happens when you're on beta.
Aside from that, it mostly does an excellent job of syncing multiple Google calendars without many problems. Google doesn't support canceled events, and this plugin doesn't have any kind of "fake" support, so canceled events just disappear. The only other problem is that it seems to stop syncing after the PC goes to sleep.
But aside from those minor things, I literally could not live without this plugin in my day-to-day work anymore, now that I need a mobile sync. It's the most important plugin I have.