What part of unmaintained is missed from the mozbackup web site. To quote.

MozBackup is not being developed anymore. There are known issues and there is no time on my side to fix all issues and develop new features. Use MozBackup only on your risk. Thanks for understanding.

The current release was "released in March 2011" so really it is exceptional that it has continued to work at all for so long.

Looking at the source, it initial upload to github was 7 years ago and there have been no edits. Given the programming language is turbo pascal there are unlikely to even be any updates. Pascal was expensive in the day to buy and is basically considered a dead language today.

There is some useful information here https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data and https://support.mozilla.org/en-US/kb/dedicated-profile-thunderbird-installation

Is there an alternative to migrate my thunderbird email from one pc to another?

Yes, see answer above. Copy everything in thunderbird profile folder to a portable hard drive, after you have downloaded your last message and switched off connection to mail server.

Install thunderbird on new pc, start it but don't do much with config. Close it down, Copy over the profile from old machine and start up, its now copied across all emails, local folders, etc.

I will keep it on my old pc for a few days just in case but will not send or receive anything from old install.

re :when I reconnected to gmail it started sucking in every email I have ever sent or received into one big all mail folder.

Gmail keeps all your emails, incoming,sent, archived - the lot, in the 'All Mail' folder. Gmail knows that this is not exactly user friendly, so they apply a type of filter - they apply 'Labels' to emails so they can 'appear' in other more useful 'folders' eg: Inbox. Sent.

If you logged on to your gmail webmail account via a browser, do you see folders (gmail calls them Labels) and do they contain emails ?

If you choose 'Settings' > 'Labels' You should see a list of the 'System Labels' and below them a list of your 'Labels' that you created. Make sure all the necessary Labels have the 'Show in imap' selected. If you do not want to see the 'All Mail' folder in Thunderbird then uncheck 'show in imap'.

In Thunderbird Gmail Imap account. What folders do you see ? Obviously you see the 'All Mail' folder -

As it is an imap mail account - Right click on imap mail account name in Folder Pane and select 'Subscribe' Click on 'Refresh' select all the folders you want to see. Click on 'subscribe' click on OK

Please note: you do not have to subscribe to see the 'All Mail' folder and if you have deselected it in the webmail account, it will no longer be available in list.

Report back on results.

on old laptop that was running 78

I preume everything was stored in default location Do not start Thunderbird. It must be closed. Locate this directory: C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\ Copy that 'Thunderbird' folder.

On new computer that is running the same version of Thunderbird. Exit Thunderbird. Access: C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\ delete that 'Thunderbird' folder Then paste the copied 'Thunderbird' folder into the 'Roaming' folder. start Thunderbird.

Thanks Toad-Hall, worked a treat