Lightning by default only supports CalDAV calendars, to my knowledge. Other online software require add-ons, most notably Google and Office 365.

I haven't tested this personally but other people online report success with this add-on.

I looked up instructions for you, this seems to be a guide to setup such sync between Thunderbird and Office 365. If it works it would be nice to come back and share your results here.

Many thanks for your reply and I have managed to set up this and downloaded my Outlook Calendar in to Thunderbird. I have to say it has been more trial and error as it did not seem to follow the guide, although this could be me as I am not familiar with Thunderbird and still trying to find where all the settings are and the guide presumes you know where they are (not helped by the screenshots being in German). But a big thank you to for your help and the add on developers

I am glad to hear that your problem has been resolved, thanks for marking the solution! This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support, and come back anytime!

ps. I've submitted a request to improve the add-on documentation to the project bug tracker.

Hello again, just following up on my request for translation of the screenshots, it's now done.

BTW the correct link is https://github.com/jobisoft/TbSync/wiki/How-to-get-started (fixed above) - I hope this is helpful to others too!

Many thanks for the update on the translation, it is working great for me. I am not sure if there are options as I have not found them as yet to have the week start on Monday, rather than Sunday and also to be able to view 2 months in the left hand pane, other than that enjoying Thunderbird and the add on