Windows 10 update should not have removed anything, but maybe you mean a reinstall or eg: updated from Win7 to Win10? Can you see a ''''windows.old'''' folder on your desktop? If yes, then it is possible your profile folder is stored in the 'windows.old' folder. You may need to make hidden files and folders visible. http://kb.mozillazine.org/Show_hidden_files_and_folders This is the usual location of profile: C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\Profiles\<Profile name>\ Make sure Thunderbird is closed. In the 'windows.old' backup folder locate the AppData\Roaming\'''Thunderbird''' folder. right click on 'Thunderbird' folder and select 'Copy' Then in Win10 locate the same location . In 'Roaming' folder, right click and select 'Paste'. It needs to overwrite any current Thunderbird folder. Start Thunderbird.