User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:101.0) Gecko/20100101 Firefox/101.0

Steps to reproduce:

Set always show attachment pane by setting initially show attachment pane option[right click on attachment pane] in message reader pane.

Navigate to a message 5 to 6 attachment. It will show all attachment.
open a pdf file new tab from attachment. return to message reader pane.

Actual results:

Attachment pane is collapsed to show only one line.

Expected results:

Attachment pane should restore previous size of Attachment pane area.

(nothing new I think)

(In reply to Magnus Melin [:mkmelin] from comment #1)

(nothing new I think)

Thanks Magnus, sadly yes!

Weird, so with "Initially show attachment pane", when returning to 3-pane tab, we keep the attachment pane open, but shrink it to one visible row of attachments - how does this even happen? I understand that message might be reloaded, but why respecting the setting only half-way?

Worse with default settings - start out with open attachment pane with several attachments, open a PDF in a tab, return to 3-pane - attachment pane closed. Need to reopen manually before proceeding to next attachment, and remember where I was.
Thunderbird is really not helpful for this basic everyday scenario :-/