On two systems I can update Tbird by Help/About Thunderbird with a link to update to latest Tbird iteration. When downloaded, it is properly installed over the current installation and profile.
However, on another system, the link offered is only to a download which, when started, does not seamlessly install over the current profile but as a wholly new installation, which often loses the profile. Is there a setting within Tbird that will change the 2nd type of installation to the first type?