That technique has worked for me.

Thank you very much for such a prompt response, David. I'll be trying it tomorrow morning and will let you know how I get on. Best wishes, M

Unfortunately, I have been unsuccessful because the files in the relevant folders are not identical.

In the screenshot attached, the older profile is on the left and the current one on the right. Should I just delete the current files and copy and paste the old ones into the same folder?

Thanks again for any advice you can give me.

I have been successful in doing exactly what you show. However, if you wish, you can use the tools>import>from a file and follow the addressbook options and then select the single abook.sqlite.

But I'm puzzled. The new profile shows the file. Are you seeing no addresses there?

I will have saved some incoming mail addresses. Would that explain it?

What happens when you select copy and paste (with Thunderbird NOT running)?

'Copy' is not available on the drop-down menu. If I use Ctrl+C followed by Ctrl+V nothing appears to happen.

'Copy as path' is present on the drop-down menu but as that is an option I haven't come across before I haven't used it. As you are kind enough to involve yourself in my problem, perhaps you have the time to explain to me in simple terms what 'Copy as path' is used for and whether it applies in this case.

Sincere thanks again for your help.

I suggest you return to earlier suggestions. The tools>import will work and the use of windows file explorer to copy will work, yet you appear to be avoiding both of those options. Thunderbird will figure out any differences. If concerned, copy the abook files in the receiving profile somewhere prior to copying in the preferred ones.