Thunderbird Calendar sync with iCal failed and doesn't allow unsubscribe. When I click on the calendar entry the "unsubscribe" option is greyed out and cannot be selected. How can I delete this?? I had started attempting to add my Apple calendar to Thunderbird following some instructions online, New calendar, from the network, Caldav, I copied and pasted the location section from using the inspector info from my web browser (firefox) as instructed by the website instructions here: https://frightanic.com/apple-mac/thunderbird-icloud-calendar-sync/ Any suggestions or help would be warmly received! Kind regards, Simon