Well, I discovered on Monday (November 17th) Google changed the calendar sign-in API. This now breaks the older version of the Provider for Google Calendar add-on. However, I was able to get all my calendars to work (for the most part) with Thunderbird/Lightning now. I linked/subscribed my school and US Holiday calendars to my main GMail account. The setup process is much simpler now with the newer version of Provider for Google Calendar. You no longer need to supply your calendar’s public/private XML address. Instead, you will be prompted to enter (or choose) the Gmail address associated with your calendar. The next…

” Although the ads are displayed by default, it is very easy to turn them off. Here is the procedure to get rid of the ads: “ Source: Gizmo’s  How to Get Rid of the Ads on the Firefox New Tab Page