Uncheck all Thunderbird options in CCleaner. Whatever you want to clean can be done from within Thunderbird. Don't let 3rd party apps mess with your Thunderbird profile.

So far, only configuration setting I have found, and used, in CCleaner, is an exclude option, where it says: "Select files, folders and registry entries you wish CCleaner to exclude". As I mentioned earlier, in that exclude section I provided the following: C;\Program Files (x86)\Mozilla Thunderbird\*.* . You mention that I should: "Uncheck all Thunderbird options in CCleaner"; if you can tell me exactly how I should do that differently from what I have already done, I would greatly appreciate it.

The location you have given is where the application itself is stored. You need instead to exclude the data, which is stored in the profile.

Help|Troubleshooting Information has a button that will take you to your profile.

See screenshot.

I have this problem and I do run Ccleaner. I saw in another message that Thunderbird creates a file called session.json which it uses to remember settings from session to session. Ccleaner deletes this file so Thunderbird doesn't remember that you want message pane off.

I told Ccleaner to exclude this file. I closed Thunderbird, I ran Ccleaner, and then I reopened Thunderbird and the message pane was gone.

For those of you who wish to use Ccleaner & Thunderbird this seems to fix the F8 message pane issue. This way Ccleaner still cleans up when you close Thunderbird but it does cause the F8 issue that you wrote about.

In Ccleaner if you click the Analyze button it will show you a summary of the files. Double click the "Thunderbird - Session" line to view the details of the files. Right click the file called "session.json" and you will see an option to add the file to the "exclude" list. This file is profile specific so if you use more than one profile you'll have to do this for each profile.

Once that file is added to the exclude list you will no longer have to hit F8 to make the message pane go away every time you open Thunderbird after running Ccleaner.