This is probably and old topic but I never found the answer. I never get the lightning calendar when Thunderbird updates to a new version. I’m not at 52 and once again the calendar is gone. It is supposed to be bundles since 38. I’ve been using Thunderbird for probably 15 years and this is one problem that I’ve never solved. I usually end up downloading lightning and it works. There is no version for 52 out there now.
So where is the bundled lightning hiding?