Rated 3 out of 5 stars

This was a great add-on until September 2014. Since then, I constantly had synchronization problems. No tweak, update, or reinstall helped to solve the problems. It took ~5 minutes to start up Thunderbird because all the reminders would pop up, remove themselves, disappear, pop up again etc. On Windows, I wasn't even able to import the calendars anymore because one window in the import dialog remained blank. Needless to say that all three software components were up-to-date versions.

I am really sorry for the developer but I had to uninstall the add-on completely. My solution to the problem is now to install the caldav calendars myself manually:

Create new calendar on network -> Caldav
Use this address and replace "your-email-address" by google email address for main calendar and by the calendar ID (under settings in brackets) for any other calendar.

https://apidata.googleusercontent.com/caldav/v2/your-email-address/events

Type in PWs and follow 2-point authentification. Done!

Takes a bit of legwork, but ended all my problems, and TB starts up in a few seconds now.

P.S.: I had to put calendar.icaljs=false in the config editor to make caldav work.

This review is for a previous version of the add-on (1.0.4). 

Rated 4 out of 5 stars

Was a lifesaver until one month ago and the only way to seamlessly syncing a calendar between a mac and a PC. One month ago the problems started with the update to 1.02. Installing version 0.32 on my mac and disabling the calendar on the PC worked for another two weeks. Now, even version 0.32 stopped working (Thunderbird 31.2.0, mac OS X). I get extremely annoying popups that ask me for the Google Calendar Login, and when I type in the password, the same popup appears a second later again, and again, and again. The only way to survive is using the crappy google browser app and the Android smartphone (which is the only device which was completely unaffected by all these problems). Interestingly, this only happens for two of my google calendars (according to Murphys law, the most important ones). Some other calendars are fine, surprisingly. Has anyone experienced similar bugs and figured out a workaround? I need this app!!! Will change to 5 stars if it works again.

Edit: Now all the calendars stopped to sync :/
Edit 2: Was able to fix my mac calendars by simply upgrading to 1.02 and entering the passwords. Thanks to the other reviewers for the instruction. Knock on wood that it keeps working. Won't try to sync with my PC for another week or so to avoid new trouble.

This review is for a previous version of the add-on (1.0.2).