If you have the calendar page (the calendar tab) in front of you and you double-click an event -- or right click on it and select 'open' -- the details of that event appear in another, smaller window headed 'Edit event: ... '. Is that what you see? And if you select the 'Event' menu in that smaller window, the 'Print' option is greyed out -- is that what you are saying? Because if that's so, then I think that's how the Thunderbird calendar is at present: it's the same on my machine too and there are various comments about it online. The print command in that small window doesn't seem to be implemented at present. However you can still print events. Close the small 'edit event' window so that you just have the normal calendar tab displayed. Then go to the main File menu at the top of the screen and select the 'Print' command at the bottom. (Or just press ctrl + p.) A dialogue will appear which offers various options for printing events -- e.g. as a list, as a weekly planner etc., and between dates that you choose.