Exit Thunderbird - this is important. Check no other versions are running via Task Manager. Thunderbird profile is here: Access: C:\Users\<user>\AppData\Roaming\'''Thunderbird''' Delete that Thunderbird folder Access: C:\Users\<user>\AppData\Local\'''Thunderbird''' Delete that Thunderbird folder Thunderbird program maybe installed in two locations, so check both: * C:Program Files\Mozilla Thunderbird * C:Program Files (x86)\Mozilla Thunderbird Delete 'Mozilla Thunderbird' folder from both locations if found in both. Delete any shortcut icons on desktop etc. Note there may be a shortcut in the Start folder. Access the 'Downloads' folder - delete all thunderbird download files. Then empty the computer 'Recycle bin' There are two possible things than can perform an update. Thunderbird can do this via the Thunderbird 'update.exe' file - this is the best to allow. In Thunderbird Menu icon > Settings > General > Updates * Select "Check for updates, but let me choose" setting Suggest - if the following checkbox is selected then uncheck/deselect it. * 'Use a background service to install updates' This will force the OS to ask if you want to allow changes. Some people find this a nuisance, but personally, I like to see the prompt because it means I can stop it if I had accidentally chosen to update. It is also possible you have other programs eg: Anti-Virus product that can perform update software on computer and they are a real pain because they may offer an update which is incorrect or even not being auto updated by Thunderbird for any reason. You would need to check computer to see if you have any updater software. I know Norton does offer auto updater so you would need to exclude Thunderbird. Thunderbird - if you installed a release version from the official download website then Thunderbird updater would never get updated to a beta version. * https://www.thunderbird.net/en-US/thunderbird/all/