Start Thunderbird using the command line (windows key +R) Thunderbird -p If your existing profile is not shown in the list of profiles so you can just select it, create a new one in the location of your existing profile. (note that the profile folder names are generally 8 random characters, a dot and the name. For example default or default- release so when creating a new profile in the old location. That is the folder to use, not specify a new name within that folder.