Rated 5 out of 5 stars

Great and obligatory add-on. I am using it with Google Calendar and with Office-365 (calendar and address book).
The only request would be: when creating an event in Office 365, the field "Show time as" can only be "busy" or "free". Meanwhile, in Outlook, the field "Display as" can be "Free", "Working elsewhere", "Tentative", "Busy", "Out of Office". When my colleagues create a meeting with Outlook, it complains only if I am "Out of Office", which I cannot do in Thunderbird + TbSync, so they invite me to meetings during my days off, entered in Thunderbird/TbSync with "Show time as: busy".

This review is for a previous version of the add-on (2.22).