The userChrome.css file is a file that can be created (or exists) in your Thunderbird profile that can be used to update the interface. I used it in the past to make the visibility better (like enabling striping). The support was always flaky. So it ...
I have the same Issue (Thunderbird 115 on Opensuse leap 15.5 using classic view on a Laptop with scaling enabled, newest message below in the Massage List panel)But also the Message List Panel jumps when deleting a message and such, changing the posi...
