Open your profile folder in a file manger and see how many copies of prefs.js you have (mostly they will include numbers.)

I am guessing you have many and actually have an issue with an antivirus program or some other software causing contention, but antivirus is the most common. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data

Thanks Matt, There are thousands of them. Do I just delete them? That seems a bit drastic.

Thanks,

Kelvin

They are just a waste of space. Thunderbird writes the prefs.js when it closes, and stores your account deletion. My guess is you need to fix the issue that is causing them first so you can actually save changes to the application.

Most of these come from antivirus program scanning in the profile folder while Thunderbird is trying to write to the files. Thunderbird response to a non accessible file is write another copy with the number with it's changes. This would be a good strategy, but Thunderbird never looks for these numbered files ever again, when it starts up it reads the prefs.js file, because now it is available and the cycle repeats.

So unless you have moved the profile folder, or have in backed to the cloud using some sort of sync, I would suggest you create an exception in your antivirus and prevent it from scanning in the Thunderbird prfile folders while Thunderbird is running and accessing files.

Then I suggest you move all of these numbered files out of the folder to another location (just as a backup if the next restart does not work.) while Thunderbird is not running, leaving only the prefs.js file and see if they continue to be created every time you close down Thunderbird.

Thank you Matt for your detailed and helpful reply. I have done as you suggested and all the issues have gone away, plus a few other niggles that may have been related. Out of interest there were over 9000 useless files.

Have a great New Year,

Kind regards,

Kelvin

you might want to have a poke around for any other numbered files. and shout if you find any. They will also probably be deletion material.

I disabled the windows search integration that I allowed in ignorance more than a decade ago and got to delete manually over 100,000 files from my profile. Made copying it much easier.

Hi, I am running Thunderbird 115.7.0 32bit and an having very similar problems. I also have old email addresses that I would like to remove plus, more seriously a server change that is affecting my current emails, as the server address won't update. Very annoying! I have located my profile folder and can find prefs1.js and also prefs numbers 2 to 7. I can't see just prefs.js. I have made an exception in McAfee antivirus to prefs1.js - tried to make a change of server but as soon as I have made it, Thunderbird asks me to restart for the changes to be applied, but they arent. I am a bit out of my depth and would be most grateful for any advice.