Note that in Lightning bug #1243407 the Lightning team confirm that there is no way to export single events in Lightning so I'm not sure why the Thunderbird team suggest that Lightning is the reason not to solve this 7 year old data-losing bug.
Note that in Lightning bug #1243407 the Lightning team confirm that there is no way to export single events in Lightning so I'm not sure why the Thunderbird team suggest that Lightning is the reason not to solve this 7 year old data-losing bug.