Make Message Pane 'width responsive' when changing Thunderbird Email window width

[timbald]

When you widen/narrow TB window in Vertical Layout mode, the Message Viewer Pane stays the same width and the Message List Pane width adapts.

Please add an option in Settings to switch this behaviour to making the Message Viewer Pane width 'responsive' instead of the Message List Pane. Keep the Folder Pane as is, unresponsive.

Use Case: Switching regularly between Laptop screen and plugged in 4K monitor. I am forever having to move the divider manually to adjust the Message List Pane, to make more/less space for the Message Viewer Pane. I keep Messahe List Pane in Table View so I do not need this Pane to widen/narrow when the Tb window width changes. 

Thank you.

[Jon]

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