Looking in my T’bird folder from the backup (obviously the same as on the PC),

I have the prefs.js file dated today 19/03/2026

I also have prefs-1.js date modified 28/03/2020 (wonder what I was doing at 13:06 that day?!) - I have many other prefs files up to 96. Most of which have 0 bytes.

What do I exactly replace and with what?

I have the prefs.js file dated today 19/03/2026

Very important: which is its size in kB?

I have many other prefs files up to 96.

Which is the size of prefs-96.js and what is its creation/modification date?

Sorry, out at a meeting this morning. Will respond this afternoon.

Sorry Mapenzi, I have had a nightmare of a day, and just arrived home!

The prefs.js file is 6.27KB prefs-96.js 0 bytes. Modified 3/3/2026

The last one with any data is prefs-92.js 39.5 KB Mod. 9/2/2026

I hope that goes someways in sorting my problem?

Sorry Mapenzi, I have had a nightmare of a day, and just arrived home!

Take your time, don't hurry!

The prefs.js file is 6.27KB

This means that it is a "virgin" prefs.js file which doesn't contain any user settings such as account settings

prefs-96.js 0 bytes. Modified 3/3/2026 The last one with any data is prefs-92.js 39.5 KB Mod. 9/2/2026

Forget all those 0 kB prefs.js files. I wonder if they have been created by some anti-virus. Rename the prefs-92.js file in prefs.js. Open your actual profile folder, then close Thunderbird. In the profile folder delete the 6.27KB prefs.js file and move the 39.5 KB prefs.js file in your profile folder. Start Thunderbird again and announce the good news...

Sorry, it is me. By now you realise you are dealing with a computing idiot!

My antivirus is Bitdefender.

Just to clarify, I have the list of all prefs files (under search results in Thunderbird)

I rename the prefs-92 - to what?

I delete the file prefs.js

I move what was prefs-92 to where exactly? Do I rename it prefs.js ?

Then reopen Thunderbird.

Sorry I need things explained in idiots language !

Bigmart, let's backup and see if we can find the simplest way to get your thunderbird working. The fact that you had 90+ prefs files indicates that you have had many problems in the past. Give us some detail info, such as whether your accounts are IMAP or POP, and how many of each? Can you do screenshots? If so, let's look at your profile. I believe these steps will get you there:

1. click help>troubleshootinginformation
2. scroll to 'profile folder' and click 'open folder'
3. you are now in the profile. if you have POP accounts, click the Mail folder and then the <POP account folder> do a screenshot of this.
4. if you have more than one POP account, repeat the above for each POP account
5. now, click the Mail|Local Folders folder and do a screenshot there.
6. post all here and then we can see exactly what you have so we can assist in recovering it with you.

If you do not have a sceenshot utility, there is a simple free one at https://www.reasyze.com/ called Sniptool. The steps to recover are a bit detailed, but not difficult. The recovery process has a few more steps if you use POP accounts. If you use IMAP accounts, it is easier to get the system back. Let us know where we can help. Once done, we can assist in ensuring that the working system can safely be transferred to new PC.