Review for Provider for Google Calendar by kharrazi
Rated 5 out of 5 stars
Deinstalled v1 and reinstalled .25 but didn't work... had to remove everything including the local files in 'calendar-data'... reinstalled .25 and couple restarts, and now it works. Plus, it magically retrieved the categories... not sure if they are stored as metadata on Google's calendar or some local DB that was preserved in the process.
However, this process takes a long time as the add-on needs to recreate it's cache file in "profile > calendar-data". It took me almost two hours.
To create your own collections, you must have a Mozilla Add-ons account.