As reported in http://forums.mozillazine.org/viewtopic.php?t=99012 and http://forums.mozillazine.org/viewtopic.php?t=116124 Sunbird doesn't show the SSL certificate confirmation dialog. I'm assuming this happens only when the SSL certificate doesn't match but it might be a general case. To see this use a brand new profile ans add this url as your remote calendar: https://boolean.is-a-geek.net/mydisk/mostafah/Calendars/Personal.ics Note that if you enter that url in Mozilla or firefox, you get the mentioned dialog.
*** This bug has been marked as a duplicate of 255903 ***
The bugspam monkeys have been set free and are feeding on Calendar :: General. Be afraid for your sanity!