In the site https://portableapps.com/support/thunderbird_portable#installing
it reads, "Just copy all of those files to the Data\profile directory within Thunderbird Portable."
It tried to overwrite the existing default profile folder, so I stopped the install and changed the name of the default profile, then migrated the profile and changed it's name to "profile" exactly as the default read.
Presumably I can delete the renamed default profile?
Recommend that this be included on the website, words to the effect that the files within the profile, not the profile "slt", be copied over which will overwrite existing profiles."