How to allow Thunderbird to render columns outside the viewbox?

When unmaximised, it’s certainly capable of this:

However, when maximised, it loses this ability:

…but it doesn’t matter much anyway, because the subject column is so compressed and impossible to uncompress:

Consequently, how do I permit the columns to render outside the viewport, like I can in KDE’s Dolphin file manager (as an example):

This sounds like a support question - the link to support is seen in Useful Thunderbird Links

1 Like

Posted at https://support.mozilla.org/en-US/questions/1463493, but it appears that Markdown isn’t accepted, so it shan’t be of much use. Thanks, though.