User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:81.0) Gecko/20100101 Firefox/81.0

Steps to reproduce:

Try to create a remote calendar.
After selecting "Network" a form with username an address is shown. After filling in these values and afterwards the password, the calendar is searched and found.

Actual results:

There is no question for the calendar type. Automatically type "ics" is created -> no access to the data of the caldav calendar, no new dates can be entered.

Expected results:

Should create correct calendar type

Helmut, your problem sounds similar to bug 1670420, but the other bug reporter mentioned that he sees "iCalendar (ICS)" as suggested calendar type.

I do not try to create an iCalendar.
I try to create a (network) caldav calendar of nextcloud. The supplied address is https://mycloud.familie-leininger.at/remote.php/dav/calendars/hlein/xxxxx but TB does not ask for the type of the calendar and creates it. It cannot synchronize nor can the created calendar be written to.

Looking into prefs.js shows that user_pref("calendar.registry.dfa83f52-4304-4564-9cf3-ee9dd4e92a8f.type", "ics"); is created, which is wrong.
After hacking the prefs file changing ics to caldav and adding some lines adapted from working caldav calendars (same nextcloud server, created with former versions of TB), it works ok.

Would imagine this must be from bug 306495

This should be fixed by bug 1652984, please reopen if I'm mistaken.