Would you be using Anti-Virus called Avast ? If yes, then Try the following: It is possible Avast is blocking a necessary link, can you do the following so it can be tested. Info at link below: Add an exception Setting a global exception will exclude individual files, folders, or websites from all scans and shields. Add as exception: '''aus.thunderbird.net''' and also '''www.thunderbird.net''' use info at link: * https://support.avast.com/en-ww/article/Antivirus-scan-exclusions Then restart Thunderbird. Hopefully, Avast will then allow the update to work properly. It would be useful to know if creating the exception fixes the problem. Clearly Avast is well aware of it or at least loads of reports on Avast forum https://forum.avast.com/index.php?topic=320195.0 https://forum.avast.com/index.php?topic=319793.0 Alternative is to switch off Anti-Virus shields and allow Thunderbird to update properly then switch them on again.