Follow the steps below to export the Celoxis Calendar to Thunderbird.

Get the URL of the Celoxis Calendar (Click option from top-right)
Copy the link.
Now, go to your Thunderbird application.
From the Events and Tasks option, click on Calendar.
Right click on the existing calendar and click on New Calendar.
Select the On the Network option and click on Next.
Select the iCalendar (ICS) option and paste the link (copied from Celoxis) in the Location box.
Click Next. Give a suitable name and a color of your choice and click on Next.
Click on Finish.

You need to have the Lightning add-on of Thunderbird installed to see the Events and Tasks option.

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