I am trying to link to a calendar hosted on www.onlinescoutmanager.co.uk. That application supplies a URL for me to paste in to a calendar application. I successfully create the new calendar in Thunderbird (i.e. I see a message saying the calendar has been created) but no events appear. The new calendar is shown greyed-out in the Calendar List. Opening its properties I can put a tick in to 'Switch this calendar on' but on clicking OK the calendar in the list appears properly for about a second before it is greyed out again. The error console shows the following: While creating services from category 'profile-after-change', could not create service for entry 'calendar-backend-loader', contract ID 'service,@mozilla.org/calendar/backend-loader;1' Expression Search: init... Use of Mutation Events is deprecated. Use MutationObserver instead.