I have a local CardDAV server running on my NAS and several different clients syncing with it. Only Thunderbird is showing the following behaviour: 1) It doesn't like syncing URLs inside contacts (e.g. "Hompage") without the "https://". That is OK but... 2) When I add the "https://" to the URL on the server side the server is inserting a backslash to escape the colon (according to vcf specs this is correct) but Thunderbird is not removing it. I.e. https://abd.def becomes https\://abc.def which in turn is considered an error and not displayed. As I wrote above other CardDav clients are removing the escape character correctly. The behaviour shows on Thunderbird version 115.16.2 (Mac) as well as 128.3.2esr (Windows).