The safest way for me is this: - close thunderbird - copy c:\users\<yourid>\appdata\roaming\thunderbird to USB drive (my ref is for windows 11, so the location may be different for win 7) - install thunderbird on new pc and exit - copy the usb folder to c:\users\<yourid>\appdata\roaming\thunderbird (this will prompt for overwrite, accept it) - start thunderbird and it should all be there.

Hello David,

 Unfortunately, your directions didn't help.  While I found the folder 'Thunderbird' in my Windows 7 PC in the 'Program Files' folder, not in the 'Appdata' folder, I was able to copy it directly to a thumb drive.  The Thunderbird folder is about 5.5GB size.
 Then I turned on the Windows 10 PC, and looked for a similar folder.  I could not find any folder named 'Appdata\Roaming' on the new PC.  While not the current (102. release) of Thunderbird was present, there is a recent release. I got a message to update to the latest version, which I did do.

So, following your instructions, I found two folders relating to Thunderbird. One is named Mozilla 'Thunderbird', the other is named 'Thunderbird'. Using the Windows drag function, I hit on the thumb drive folder, 'Thunderbird', then dragged it to both the Mozilla Thunderbird folder and then to the Thunderbird folder on the 10 PC. After making the copies, I opened Thunderbird on the PC. NOTHING was there ..... only the initial folders which appear on the left side of the screen.

 So, I went to the Tools menu, clicked on the Import option.  I followed the prompts .... one option is to transfer the files from an external source.  I clicked on it, located the thumb drive and selected it.  When it showed in the window, I clicked on the Thunberbird folder, then pressed the Next button, and that's when I got an error message at the top, stating that there is a problem:  "Import operation failed unexpectedly.  More information may be available in the Error Console."

So, now I am no further along than I was before I started.

Furthermore, the 10 PC has one of my e-mail addresses listed, but when I tried to open it (in the 10 PC), instead a Gmail window opens asking for the e-mail address and the password. The e-mail address that appears in the box is correct .... I've checked it several times, but when I type in the password, Gmail sends back a message that it's an incorrect password. This is IMPOSSIBLE since I'm using this same e-mail address to converse with you, and I use it every day to converse with others, and I can go to the native Gmail e-mail app, and it works there also. So, WHY it doesn't allow me to open the e-mail address in Thunderbird on the 10 PC is a total mystery!!!! Please help! I need to move off this 7 PC before it dies completely & I lose all the important data that is stored on this PC. Finally, I'm going to have the same situation with FIREFOX, since that is my primary internet access application also, and based on these problems, I'm very fearful that I will have the same problems porting over all the web links that are in FIREFOX on the 7 to the 10. Thank you.

On the Win 10 PC, In windows File Explorer, click View>Show>Hidden items . Then you will be able to see the appdata\roamimg\thunerbird folder.

When setting up Gmail, be sure to set auth as OAUTH2 and omit password during setup. Gmail will provide a new password for thunderbird for you.