Rated 4 out of 5 stars
This is a great add-on for the default Lightning calendar, but as of today (20 June, but probably earlier) the add-on requires me to logon EVERY time I load up Thunderbird. This is pretty much a no-go for myself with about 6 different calendars, and a 20 character password. Must try harder!
(edit) After several tests, it seems that updating must have screwed something up, but uninstalling the provider, then re-installing it, seems to fix it.