Why doesn't the latest version of Lightning Calendar, version 5.4, not work with Thunderbird version 52.9.1 on Windows 7? It's enabled on the Tab that came up as Add-on Manager, under the Extensions menu. This did work with the previous version. Now, the Lightning Calendar is not visible on the Tab, but the Calendar Reminders, still work on their schedule. We just can't see the Calendar, add events to it, or edit the ones that are on the Calendar. 1. Does Thunderbird need an update? 2. Does Lightning Calendar need an update? 3. What are the newest versions of each that will work together? 4. If they exist, where are each of them located? I uploaded an image of what the Tab Extensions looks like.