68.1 loses preferred message window size
Every time Thunderbird 68.1 (on a Windows 10/1903 machine) is started, the message windows (both read and write) pop "back" to an excessive size that covers nearly the entire vertical screen height and WAAAAAAAAAY more than either message width or toolbar width. Manually changing the size to something more usable persists only during that session of Thunderbird... and not across window types (that is, changing the read window doesn't change the write window's size, and vice versa).
This is a new problem in 68.1; I never had it before, and indeed never had it even with major updates.
I have other machines running Windows 7, but do not use Thunderbird on those machines often enough to determine whether this is a Windows 10 problem.
Alle svar (4)
Start and restart a few times in safe mode (hold Shift when you launch TB). Do the windows look different?
No effect (that is, starting three times in safe mode did not enable Thunderbird to remember the proper window size, which I had tried before I posted this... and one wonders why 68.1 changed the window size in the first place).
Just as an aside: It's usually a very bad sign when the first resort for an unpredicted behavior is to do something with safe mode. I'm going to be very skeptical of further, similar suggestions.
TB 68 didn't change window sizes on my system, or those of most users, so your problem is probably due to some issue in the profile folder. Delete or rename session.json from the profile folder and see if it helps.
For your information, starting in safe mode is usually the first and simplest step in diagnosing TB issues:
Deleting session.json had no effect. I had also tried that before posting this.
And since I know what the next debugging step should be, there's only limited set of extensions installed: Lightning and Lightning Calendar Tabs; CompactHeader; ImportExportTools NG; No Message Pane Sorting by Mouse; Phoenity Buttons; and Send Later. Of course, Safe Mode temporarily disabled them (but did not solve the problem), so they shouldn't be the focus of future notes.