If you want calendar events shared between computers, it's neater IMHO to sync those computers to a shared online calendar. Lightning works well with Google Calendar and I've had it work just as well with other calendars, such as that offered by GMX, using CalDav. If you go down the route of moving data files to and fro, you'll constantly be playing catch-up, and struggling to keep track of which one overrules the other. The export function is asking you where you want to save the exported data to. It already knows where to get it from when you selected which calendar to export. To put everything on a new computer, I'd copy the old one's profile to the new one, rather than your piecemeal approach. https://support.mozilla.org/en-US/kb/profiles-tb