Are you using anything such as CCleaner that might be unhelpfully deleting useful files?

No, I'm not using CCleaner - I've been over that road several months ago. And I've tried every other suggestion offered on the subject. I've been involved with computers and data processing since 1961 - programing, systems design, etc. etc. I'm just trying to find a point to modify the TB programs to simply change a minor annoyance.

I have a theory that on occasion Thunderbird fails to read settings, with the result that the missed settings can revert to their default values. We see, for instance, accounts resetting to plain text rather than HTML, or SSL/TLS being turned off, or toolbars appearing or disappearing. I wonder if failing to read the "off" setting for the Message Pane from session.json is another manifestation of this?

As an example, I have the Folder Pane, the Message Pane and the QuickFilter Bar visible, all by choice, and perhaps since these are defaults, they never misbehave.

You could try launching Thunderbird from a batch file that copies over a standard version of the session.json file before running Thunderbird itself, though of course you'd be thwarting its intended purpose of recording any changes made by you during the previous session. You might also make session.json read-only, with the same caveat and the additional problem that failure to write to it when Thunderbird closed would almost certainly generate another error. But if Thunderbird is truly failing to read this file, then whatever steps you take to ensure the session.json file is correct when you start Thunderbird may be fruitless.

A smarter approach would be, rather than just substituting a prepared copy of session.json, to read the existing session.json, and fix-up just the entries of relevance, leaving other changes in place, and recording to a log file what changes had been made. Of course this would require some programming or scripting and of course, none of this fiddling about should be necessary. But it could provide evidence of files changing or being mis-read, since you'd have certainty that the correct settings were in place whenever Thunderbird is started.

Thanks for the response.

I've tried making sessions.json "read only" - TB just ignores that setting.

I guess I'll have to use the batch file approach. I have built a "sessions.json.txt" in the profile folder with the necessary changes. I can then open the profile folder, click on the ".txt" file, which opens "notebook" with the 'txt file loaded. I can then "save as - session.json" and start TB. I assume these steps will work as a batch file.

It would be nice if we could simply FIX TB to eliminate the problem.

Thanks again

L

Again, none of this should be necessary. But I'm interested in gathering evidence of these spontaneous changes, and recording changes to the session.json file would be a good starting point.

I have been playing with a python script to implement my idea of looking for the setting being switched on, and then editing it to off and recording the event in a log file. This leaves other legitimate changes to session.json in place. This works for now with the Message Pane, but parsing and adjusting the QuickFilter settings needs a bit more thought.

None of this changes the user's ability to change, accidentally or otherwise, the settings in Thunderbird itself. If you have made the message pane go away, it comes back if the splitter is dragged up. So you don't need to actively visit and change the settings; the act of dragging is sufficient. Most people who want to disable the message pane (usually because of unfounded fear of malware getting in) would find this unsatisfactory.

For myself, I couldn't imagine using Thunderbird without the message pane or the quickfilter. They are just too darn useful.

I have been playing with this for the last few days - and I have another eye-opener for you. I made the changes I described above to the session,json file - then right clicked on the file, selected properties and went to the 'security' tab. I then changed ALL the permissions to 'Deny', went back to the 'General' tab and made the item 'Read Only'. Saved the folder and opened TB. It worked just fine - the filter bar and the message pane were gone.

I took care of some emails and closed TB. When I opened TB again, it all was back. So I went back and checked the properties of Session,json. GUESS WHAT!! All of the permissions had been restored, and the 'Read Only' was unchecked. TB had simply ignored all of the changed settings, and put it all back the way it was.

Do the folks at Moziolla ever read these postings? Do they realize that TB does not recognize these settings (and why even have them available if they do nothing)? Is there even a chance that they might make a change to the program to solve the problem?