Hi forum

today all over sudden the sync via Caldav to Thunderbird (Lightning and Caldav Plugin) stopped working. I know a lot of people here might say the same "I have not changed anything" ;-) but I really didn't change one piece on my Zimbra for the last weeks. I use the following zimbra version
su - zimbra
[zimbra@webmail1 ~]$ zmcontrol -v
Release 8.0.6_GA_5922.RHEL6_64_20131203103705 RHEL6_64 FOSS edition.
I use a URL like this to access caldav: https://mydomain.tld:4433/dav/user@mydomain.tld/Calendar
Port 4433 is forwarded to zimbra's LAN IP on port 443. But I also tried with https://lan-name/dav/user@mydomain.tld/Calendar
Same effect: Thunderbird cannot access the calendar. The strange thing is that TB does not even ask for the password. I deleted the stored password from TBs password-manager but does not help. TB does not ask for a password. I deleted the calendar from TB, removed and reinstalled the two plugins (lightning and caldav) and at the end even re-installed Thunderbird but all does not help.
But when I call one of the URLs above in the browser I get asked for a password as expected and I get the txt file with the calendar definition stuff. I use TB 24.5.0 on fedora 20

Thanks a lot for any input as I'm running out of ideas :-)