User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:60.0) Gecko/20100101 Firefox/60.0 Steps to reproduce: 1. Start Thunderbird 60.2.1 (32-bit) 2. Options -> Composition -> General 3. Uncheck "Use Paragraph format instead of Body Text by default" -> OK 4. Close Thunderbird 5. Start Thunderbird Actual results: The Option "Use Paragraph format instead of Body Text by default" is still checked Expected results: The Option "Use Paragraph format instead of Body Text by default" should be in the state the user set it, even after restart

Does it happen with Thunderbird started in safe mode?

Yes. Verified with and without "Disable all Add-Ons".

I can not replicate with Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

I also can not replicate with TB 60.2.1 on Windows 10, or with Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

Ok, this info pushed me in the right direction. Deinstalled Thunderbird, deleted the entire profile-directory and finally reinstalled Thunderbird. Now it saves the state of this flag. Could be a problem with some of the previous versions, because I upgraded TB everytime since version 45 and made no fresh install... So you can close this case, thx!

Most likely a profile upgrade problem like in bug 1489976.