First, I have no solution. The problem appears to be something preventing Thunderbird from saving files to the harddrive. You create an account and it works fine, and it's not there on a restart. That happens because Thunderbird was unable to update the prefs.js file. Further proof is that you have many prefs files. I don't know if it's an antivirus, VPN, or what, but there is an interruption to Thunderbird that is causing this.

Thanks for the suggestion. How do I find what causes TB to keep making new prefs.js files, and not using the existing one ?

As I mentioned, I don't know. Thunderbird issues a save to prefs.js but it fails, causing the creation of prefs-1.js. You might look at antivirus or VPN or firewall. I am not that technical to know the mechanics of digging through that.

Thanks, so I'm hoping some wizard tells me how to do that

Please provide results for the following test on your system

1. Does Thunderbird work as expected in Thunderbird troubleshooting mode?
2. Does Thunderbird work as expected with your OS started in safe mode with Networking. Instructions for each operating system: Windows 10/11, Windows 8, Windows 7, OSX

Maybe I wasn't clear in my points 1 and 2 1. In troubleshooting mode TB works OK with both existing account and newly added account, but the latter still disappears on closing; 2. I should have written I tried Windows safe mode 'with networking to no avail. Should I try renaming file prefs-1.js as prefs.js? Paul

Use Windows to check whether prefs.js is read-only.

Thanks -- will do tomorrow asap (Have no prefs.js proper; only prefs-1.js after I removed -2 thru -22; should I rename it prefs.js first?)

Paul back again; thanks for the help. To repeat: I had no "proper" prefs file, but 22 prefs-xx ones; removed 21 of them, keeping only prefs-1.js. It is not read-only, was created/modified April 2020, accessed April 2022, occupies 64K, and is checked "ready for archiving". Should I look up the 21 others I set aside and retrieve only the most recent one? Or rename this one as simply prefs.js?

Generally, the most reliable one will be the one with the highest number. the prefs-1 will not have any changes done since 2022. I have this 'feeling' that an attempt to rename to prefs.js will fail, being told that it already exists. Just my guess.

Paul back again; thanks for the help. To repeat: I had no "proper" prefs file, but 22 prefs-xx ones; removed 21 of them, keeping only prefs-1.js. It is not read-only, was created/modified April 2020, accessed April 2022, occupies 64K, and is checked "ready for archiving". Should I look up the 21 others I set aside and retrieve only the most recent one? Or rename this one as simply prefs.js?

I think it would be interesting to compare the files and see whether there have in fact been any changes. https://winmerge.org/ has this. (I have not tried it) So does notepad++

Immediately after adding an account (immediately after startup), check Error Console (ctrl+shift+J) for warnings and errors.

Bugzilla query: https://mzl.la/4e4UDbG

1. I replaced prefs-1.js with the most recent (-22, last modified August 2024, 72K, not read-only, "ready for archiving". Problem remains (i.e. newly added account works fine but disappears upon closing). Tried renaming the file as just pref.js but that was not accepted, as David expected. 2. I tried the "error" suggestion "right after startup" but here the problem is that starting TB now always triggers my default browser (Firefox) to pop up a "please donate" page ... 3. in anticipation of a "comparison" suggested by Wayne, I set aside (on a thumb drive) two files I named "prefs-22before.js" and "prefs-22after.js" adding the new account (which, as always, worked fine until closed). I did look up winmerge but find it personally daunting. Rather try easier things first, such as 4. how do I know if the connection with the provider is encrypted? (I doubt it b/c I'm clearly tracked), or 5. how do I check for antivirus interference? I'm a layperson in such matters 6. to a layperson, the possibility of "external interference" looks less plausible. To me, the existing account works fine, adding an account no problem, added account works fine etc. but then at closing the program "forgets" to save some settings. Seems like a bug inside the program rather than outside.