The first day after the update, the icons for calendar and tasks were showing but didn't do anything. Today, the icons don't even show up. I tried to reinstall Lightning as mentioned on several threads. But after restartng, it still shows "Lightning will be installed after you restart Thunderbird - restart now or undo." So I clicked on restart now; it restarts, but still shows the same message to restart. I closed it completely and opened it again. Same thing. I was using Google calendar with the Provider for Google Calendar add-on, and it disappeared after the update, too; I reinstalled it and am getting the same message for it. gContactsync is still there from before the update and working fine.