Timemachine is used to backup files and folders, so it is assumed this had a backup of your profile name folders. Typically you would backup the 'Thunderbird' folder as it would contain everything. Profile folders are located here: ~/Library/Thunderbird/Profiles/<Profile name>/

The tilde character (~) refers to the current user's Home folder, so ~/Library is the /Macintosh HD/Users/<username>/Library folder.

I presume you used that backup.

However, the MAC 'Contacts Address Book' is stored : ~/Library/Application Support/AddressBook

Good info to help locate: https://www.cisdem.com/resource/restore-contacts-from-time-machine.html https://www.lifewire.com/back-up-or-move-contacts-or-address-book-data-2260801

You need to get the Contacts in MAC Address Book restored from backup

Then make sure Thunderbird can access it: https://support.apple.com/en-gb/guide/mac-help/mh43711/10.14/mac/10.14 https://www.howtogeek.com/361707/how-macos-mojaves-privacy-protection-works/

If you do not have any contacts in the MAC Contact address book, then you are not going to see anything in Thunderbird when it looks at that MAC address book.

Thanks for that. I have already tried a few things, however, because I had to wipe my Hard Drive and get a new copy of Monterey you cannot go back in TimeMachine for things as, there is no enclosing folder and it then goes into My Documents, which I do not know if I can do anything with that?

It all seems to be empty, whereas, the emails lists and contacts I have lost are in specific groups that I need, which are about three in number that would take me a long time to rebuild if I have to do it one by one. They were there before I wiped my hard drive, but as Thunderbird is not an Apple App and, also not a main one, you have to rebuild somehow by other means.

If you make regular backups of the TB profile folder to an external location, it won't depend on Time Machine. Backing up and restoring the address books is a simple operation, if that information is critical, or it's possible to sync with contacts stored in iCloud or gmail etc.

Apple techie's had asked me to disconnect my iCloud account during recent months as, I have had an ongoing problem with smtp's going out on my broadband although, my internet and IMAP emails all function. I have had various engineers sent out and an Eero mesh system given to me by TalkTalk, but all to no avail. It all started when I was given Fibre and more lately Fibre plus from TalkTalk. I have been with them for decades, but nobody can resolve the issue thius far.

I have redone manually the group email lists that were missing in Thunderbird by adding the relevant 80 0dd email addresses that had disappeared by adding them to the personal email and or collected email address book in Thunderbird and deleting all of the Thunderbird empty lists in Apple Contacts and will tie up the Mac OS contacts across both platforms so, that they are current.

Thanks for all suggestions, however, without the iCloud back-ups and with a fresh Monterey download and building a completely new set-up, I thought that it was best to just resolve the issues manually and move on :)