Exactly what are you doing, what is happening and what do you expect to happen?

You assertion that none of the export methods work may be the case for you. But not for most folks. So the first thing that needs to occur is to establish exactly what you are doing. Is what you are exporting your calendar stored locally or a network calendar stored on the web? I notice I can not export the US footy calendar that is linked from my google account where it is linked for elsewhere. I can export other calendars

Matt, sorry if my earlier comments appeared snarky.

I am simply trying to export my calendar (stored locally) as an .ics file so that I can move it to Thunderbird on a new PC. I've tried on a Windows desktop and a laptop as well as a Linux desktop with same results. I contend that the instructions at https://support.mozilla.org/en-US/kb/exporting-and-sharing-a-calendar do not work as described. Clicking on Tools<Export brings up a dialogue box to export the entire profile which I don't need. If I click on Events and Tasks<Export a dialogue box appears titled "Select Calendar" but if I select and click "OK" nothing happens. If I right click on the calendar in the left pane and select Export nothing happens. I've tried on a Windows desktop and a laptop as well as a Linux desktop with same results. </p>

I am happy to share screen shots and/or videos if that will help.

Based on the previous discussions on this Forum, others have had the same problem. See https://support.mozilla.org/en-US/questions/1386092.

Can't the calendar data files be moved into the new folder (after saving a copy of the ones that exist) and see if it works? Is there some reason why that's a 'no-no'?