Steps to reproduce:

Go to an email with attachment(s). You will have to click on the unnecessary bottom bar to reveal the attachments. Open one, e.g. a PDF, which will open in another tab.
Go back to the main tab with the email view. Now the bottom bar is collapsed again and you'll need to open it; this process repeats.
This adds a lot of friction and is time consuming.

Expected results:

Let the attachment bar be auto-revealing, or at least remember its last state (opposing to the current behaviour where it will always collapse).
Or get rid of the collapsing thing alltogether, it's not needed and cluttering the UI.

Thanks quadronom, that's annoying indeed. It's a known, age-old design problem which we'll fix in bug 1729379, expected for mid 2023.

However, in the mean time, here's how to make things a bit better and reduce the annoyance:

• Right-click on the attachments header bar > Check "Initially Show Attachments Pane"

This will keep the attachment pane always open, even when returning from other tabs, which is much better for your scenario. However, it will still shrink to 1 line of attachments shown even if there are more, something wrong with that mechanism, too, but it'll probably all need to wait for the big redemption in the next major release of Thunderbird.

Thanks for the workaround! It never appeared to me that right clicking the bar itself would do anything, so the discovery of this feature is like non-existing. But great something like this is there.