User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:93.0) Gecko/20100101 Firefox/93.0

Steps to reproduce:

If you receive an email that has many attachments, and expand the attachments pane to view them, open the first attachment, read it, and close it, the attachment pane has collapsed again. This makes it tedious to read each attachment in turn.

Expected results:

The email's attachment pane should stay open if the user previously opened it.

Hey Alistair, that feels like playing cat and mouse!
You are talking about PDF attachments, right?
As a workaround, you could Ctrl+Click several attachments, then right-click on selection > Open, that will open multiple PDFs in tabs, so you won't need to go back to the attachment pane for each one.

STR

• view message with multiple attachments, including some PDFs, in 3-pane msg reader
• double-click to view PDF 1 -> opens in a TB tab
• close TB tab
• return to main 3-pane tab and observe attachment pane state

Actual

• whenever returning from any TB tab (e.g. PDF-tab) to main 3-pane tab, the attachment pane will be collapsed again
• Tedious to open PDF attachments one at a time

Expected

• Tabs should always preserve their previous state upon returning
• Don't collapse attachment pane when returning from a TB tab to main 3-pane tab

Aleca, any ideas?

Indeed, if the currently selected message is not changed, the state of opened/collapsed panes should be maintained.

For what I can see, it seems that the message is reloaded whenever the tab is changed.
Is this on purpose?
Are we "unloading" the message pane when the tab is changed?

Pinging Magnus to see if he has better insight on this.

It's an ancient problem: Bug 487386. Will be solved with Geoff's new 3pane implementation.
I suppose this is really just a duplicate of that.

(In reply to Thomas D. (:thomas8) from bug 1774582 comment #2)

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 :-/

Expanding the attachment pane to show them all would fix this, see bug 1789283.
That way, the attachment pane could actually be made non resizable and we would just need to remember if it's opened or collapsed.

(In reply to Magnus Melin [:mkmelin] from comment #4)

It's an ancient problem: Bug 487386. Will be solved with Geoff's new 3pane implementation.
I suppose this is really just a duplicate of that.

Alistair, do you agree this is gone in version 115?

Yes, this now appears to work correctly on 118.0b1. Thank you!