There is a list of diagnostic steps for this kind of problem:

http://kb.mozillazine.org/Toolbar_or_windows_layout_not_working

Since safe mode doesn't help, you can probably rule out the suggestion to delete xulstore.json. I think you might have some success by deleting directorytree.json, foldertree.json, search.json and session.json, as explained in the section beginning "If deleting xulstore.json doesn't help,...".

Do you have any userChrome.css or userContent.css files?

If the above doesn't help, it might be faster to create a new profile and transfer data from the old profile.

Thank you for the quick reply. "Do you have any userChrome.css or userContent.css files?" Yes, I have a "userContent.css" It's 2 bytes.

I deleted " directorytree.json, foldertree.json, search.json and session.json" and that appears to work. Thank you very much.

I hesitate to mark this solved as yet because what I didn't mention in the post was this problem fixed itself a couple of times before going back to this behavior and staying there. Rebooting Thunderbird and/or the computer provided a temporary fix. I'm not sure why or how that could happen, but right now everything looks good. This last time rebooting did nothing, but deleting the folders did the trick.If it stays that way for a couple of days I'll come back and mark it solved.

Thanks again, Len MAYBE IMPORTANT-- I had the profile folder sitting open on the desktop to delete the files and I noticed that a file named prefs-1.??? flashed in and out several times between the "prefs.js" and the prefs.zal" files. The question marks mean that I didn't have time to read the file type before it disappeared maybe "qs" ? I don't know if this is important but is seems like odd behavior. It's stopped now.

I just clicked on the "prefs.js" file in my open Thunderbird profile to see what it was and it opened a strange looking FIREFOX window with a restore session box. How can a Thunderbird profile open Firefox? Maybe nothing, but it seems very strange. Maybe I should delete it too? Thanks again, Len

zeterian-gmail said

I just clicked on the "prefs.js" file in my open Thunderbird profile to see what it was and it opened a strange looking FIREFOX window with a restore session box. How can a Thunderbird profile open Firefox? Maybe nothing, but it seems very strange. Maybe I should delete it too? Thanks again, Len

The file extension is JS. whatever your operating system has registered to handle files of that type will open when it is double clicked.

It is NOT an issue.

Have you tried pressing F8? It toggles the reading pane off and on. I would be lost without mine!

Hi, as I feared it's back. The flashing from half page of emails to full page same as before. I looked in the profile folder and "foldertree.json, search.json and session.json" are back. FolderTree went from 4KB to 11KB, session.json stayed the same at 1KB, and I have a "search.json.mozlz4 file that I don't think was there before and replaced the search.json file that I deleted. It's 5KB the old search.json was 17KB. I assume I can delete delete them again but I'd like to find out what's causing this.

This may or may not be related but when I'm posting this hitting shift + any letter opens a Firefox IDE window telling me it's unable to load project list. I haven't had this happen writing elsewhere.

Thanks for any help. Len

Good to know about Firefox opening .json files. Pressing F8 in Thunderbird doesn't do anything though. Thanks. Len

You deleted a collection of cache files and they came back when Thunderbird restarted. Exactly as they should.

Have you tried pressing F8? to turn the reading pane back on?

BTW only the session.json file is really involved with the display of the reading pane.

Pressing F8 doesn't do anything, though It has stabilized to nprmal right now. I got through a couple 3 computer reboots before anything happened. Len

I just wanted to add that after I deleted the cache files I closed and restarted Thunderbird a couple of times without them coming back. Thanks, Len

zeterian-gmail said

I just wanted to add that after I deleted the cache files I closed and restarted Thunderbird a couple of times without them coming back. Thanks, Len

Just to be clear - TB must be closed before you delete or rename any profile files.

Yes, I closed it first, then checked the profile folder again after I had closed and reopened it a couple times, then checked the profile folder. I took 2 days for them to reappear and the window pane flashing to come back.

The window pane flashing that came back on the 4th went away on it's own the next day and hasn't returned so I guess it's fixed. I just think it's odd that it comes and goes by itself. I can't think of anything I did to cause or fix it this time. The first time it flashed fow several days. I do want to give everyone a big THANKS for all the help. Thanks again; Len

I think I just resurrected part of my problem. I tried pressing F8 again like Matt mentioned and nothing happened as before, then I hit 8, just the number and the message pane disappeared and the folder pane enlarged to the whole window and won't go back. No flashing but no message pane either. I tried restarting Thunderbird to no avail. I guess I'll try deleting those files in the profile again. I didn't expect hitting 8 to do anything, boy was I wrong. Hitting any of the f? keys or numbers doesn't help.

I want to thank you again for the help. I post tomorrow with results from deleting the files. Len

I tried deleting the files again, made it worse. Instead of the folder pane staying full screen it's back to flashing from full to half screen with the message pane rapidly appearing and disappearing again. If it doesn't clear up I guess I'll have to create a new profile. Thanks for the help any ideas would be appreciated. Len