I have found a workaround for the problem.
The workaround may suggest where the problem lies.
The workaround is: disable drawing on tabs in titlebar; maximise the main window; close Thunderbird; re-enable drawing of tabs in titlebar. Result: Thunderbird will now open maximised.
I have found a workaround for the problem.
The workaround may suggest where the problem lies.
The workaround is: disable drawing on tabs in titlebar; maximise the main window; close Thunderbird; re-enable drawing of tabs in titlebar. Result: Thunderbird will now open maximised.