TB Update 38.5.1 made Lightning dis-appear.
TB 38.5.1update wiped out Lightning. No sign of it. no lightning under add-on extensions. Tried downloading Lightning 4.0.5.2 and installing. Nothing happens.
Opaite Mbohovái (1)
Go to Thunderbird profile directory shown at Help | Troubleshooting.
Close thunderbird.
Delete {e2fda1a4-762b-4020-b5ad-a41df1933103}.xpi and {e2fda1a4-762b-4020-b5ad-a41df1933103} directory
Start Thunderbird. Install calendar addon.