User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.105 Safari/537.36

Steps to reproduce:

With multiple file attachments, attempts to reorder the attachments with a mouse drag and drop fail to change the attachment order. The attachment order insert marker moves to the dragged location as expected, but when the mouse is released, the attachment order remains as it was originally.

Actual results:

The attachment order stayed the same.

Expected results:

The attachment order should have changed.

Good find, Karen, thank you!
Confirming on win10, 78.1.1 (64-bit).

In the meantime, please use Reorder Attachments from context menu and/or keyboard shortcuts as advertised on Reorder attachments panel (Alt+Up, alt+Down, Alt+Home, Alt+End etc.). Keyboard shortcuts work without the panel, but also while the panel is open, which is a good way of learning them.

Strangely, nothing in error console.

Confirming win10, 78.1.1 (64-bit). Thanks for the heads up on the alt+key workarounds.

Alice, would you do us the favour to find the regression. Just add 3+ attachments to a new message and then try to drag the last one first.

Regression window:
https://hg.mozilla.org/comm-central/pushloghtml?fromchange=3b281b9a0b409202fd555893700881cfc1e65ce4&tochange=4e33fd9bc7b6cb8a04c50c1993b8e3f9184b0b9b
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=f7f534f08b4827c90ed4ec421c14355cb81dfaaa&tochange=82d1507999fd21f798d473c2b9e8ad5d8947ba20

Suspect:
7ed85c4ae6bf85b278c73cbced91bb829a0c93fa Khushil Mistry — Bug 1226362 - Use HTML Drag and Drop API in Messenger. r=mkmelin

Thanks so much, Alice, let's make it so.

Does this code fault also impact the ability to mouse click in the attachment window and add attachments?

(In reply to Wayne Mery (:wsmwk) from comment #8)

Does this code fault also impact the ability to mouse click in the attachment window and add attachments?

No, still works for empty attachment pane, then unexpectedly fails if you try the same trick with attachments present, that's bug 1656180. Most convenient, big no-brain click target, works perfectly in TB68, not harmful in any way (we can protect ctrl/shift selection misclicks a bit more), not sure why someone would want to break that and create ux-inconsistency...

Pushed by geoff@darktrojan.net:
https://hg.mozilla.org/comm-central/rev/2e4a327e4e26
Fix order of file attachments cannot be changed by drag and drop. r=mkmelin

Comment on attachment 9169392 [details] [diff] [review]
Bug-1658114-DnD-attachments-pane-0.patch

[Approval Request Comment]
Regression caused by (bug #): bug 1226362
User impact if declined: can't reorder attachments
Testing completed (on c-c, etc.): yes.
Risk to taking this patch (and alternatives if risky): small patch, small risk

Comment on attachment 9169392 [details] [diff] [review]
Bug-1658114-DnD-attachments-pane-0.patch

[Triage Comment]
Approved for beta
Approved for esr78

Thunderbird 80.0b4:
https://hg.mozilla.org/releases/comm-beta/rev/a541f828bfc7

Thunderbird 78.2.0:
https://hg.mozilla.org/releases/comm-esr78/rev/264d0766cae0

I was able to change the order of attachments using drag and drop using TB 80.0b4 on Ubuntu 18.04.4 LTS.