calendar disappeared from thunderbird

Ubuntu 16.04. Thunderbird 60.2.1 (64 bits) Calendar has disappeared.

That change in Thunderbird, which is automatically updated, costed me 1 hour of research and work. How many hours these guys took from ppl around the world? Is seems they just don't care. Because, maybe, they become big.

For now: 
1. Remove Lighting from Thunderbird.
2. Close Thunderbird
3. sudo apt install xul-ext-lightning
4. Start Thunderbird again.

Calendar is here again.

Or... you may try to download and install appropriate version of Lighting:
- versions: https://developer.mozilla.org/en-US/docs/Mozilla/Calendar/Calendar_Versions#Stable_Releases
- downloads: https://ftp.mozilla.org/pub/calendar/lightning/candidates/

For tomorrow, seriously consider different pim tool, because you may find yourself in not comfortable situation.

Howto remove a broken add-on from Thunderbird

When you add a broken add-on to Thunderbird it may cause Thunderbird to prevent you from doing anything, so you cannot remove add-on which is causes Thunderbird crash. Write in terminal:

thunderbird -safe-mode

Then you can remove and add-on.
source

Thunderbird - jedno konto dwa komputery

Czy mogę korzystać ze swojego konta pocztowego na Thunderbird z dwóch różnych komputerów?

Tak.

1. Skopiuj katalog profilu na nośnik zewnętrzny np. pendrive. Katalog profilu jest wskazany w ~/.thundebird/profiles.ini

2. Podłącz nośnik zewnętrzny do dowolnego komputera z Thunderbirdem.

3. Uruchom na tym komputerze Thunderbirda poleceniem:
thunderbird -profile "pełna ścieżka dostępu do katalogu profilu"

Można na stałe ustawić korzystanie z poczty na zewnętrznym nośniku. Należy wówczas wpisać w ~/.thunderbird/profiles.ini w sekcji [Profile0] ścieżkę przez podstawienie Path=..... , oraz IsRelative=0