Great addon, with bugs Rated 2 out of 5 stars
I am using Lightning with the latest Windows Thunderbird, synced with Google Calendar via CalDAV.
The addon is great and powerful. I encountered a few problems though:
1) Many docs available online are outdated and suggest to download an addon to sync with Google Calendar instead of using CalDAV. I had problems with that addon.
2) For some reason, if offline (and that includes in the very first seconds after resuming the laptop from sleep, i.e. several times a day), Lightning likes to open up a dialog that looks like a browser page, pointing at "accounts.google.com/o/oauth2/...". The dialog of course gives a 404-styled page "Server not found" as the computer is offline. The user then has to either close this dialog, or hit F5, and "Accept" to tell Google (for the n-th time) that Lightning has the authorization to access my calendar. I assume that this window is supposed to stay invisible and succeed silently, but if offline, it fails non-silently. Note that TB's Password Manager confirms that my Google Calendar password is known and stored.