STR:

1. Click the header of a column in the message list to change the sort order of your emails. Make sure that it's not the already selected column.

Actual:

The message list animates to a new position. I am not sure if this animation is really desired. At least it's unexpected to me and was not there in Thunderbird 102.

Expected:

No animated change of the position.

If I understand you correctly, the effect should disappear when you turn off "smooth scrolling".

Settings -> /General\ -> Scrolling
[ ] use smooth scrolling

While I could do that I don't want to disable smooth scrolling at all. Even with this option enabled I don't think that the animation is expected in this particular situation - and it was not animated in Thunderbird 102 either.

Could you please first confirm that smooth scrolling is the culprit? So the bug disappears when you turn it off.

Then we don't need to look for another cause.

Of course, you are free to turn it on again later.

Yes, it only happens with enabled smooth scrolling.

This was done on purpose and only happens if a message is currently selected in the message list.
We always try to guarantee that the currently selected message is visible in the list viewport, and if the user changes the sort order causing that message to be moved outside of the visible viewport, we scroll to ensure its visibility.
This is more desirable than losing the position of your currently selected message.

I'm inclined to mark this as WONTFIX, but I'm curious if there's any potential counter argument we haven't considered.
What would be the case scenario in which we shouldn't ensure the currently selected message remains visible?

Please see the following video for a comparison between Thunderbird 102 and Thunderbird 115/Daily: https://www.youtube.com/watch?v=vgX6h7ooLL8

This issue is not about keeping the selected message visible, that was already the case in Thunderbird 102 and is a good thing. This issue is about the animated scrolling. The scrolling was not animated in Thunderbird 102 and I really think it shouldn't be animated because it's more annoying than a useful transition, especially since there is sometimes a white flash (as you can best see at the end of the video).

Thanks for the video.
I understood the problem, but that's indeed not a regression per se.
The behaviour is identical to 102, but since 102 used the XUL tree which didn't support smooth scrolling, the sorting and "scrolling" to the selected message was happening instantaneously.

We might consider disabling smooth scrolling when the user changes the sorting order, but that's not a regression and not a bug, it works as intended.

There's also the consideration of "how many times per day users change the sorting order?".
We can safely assume that changing the sorting key and direction is not a common action and once users set their preferred layout, they won't interact with that anymore. So, is it worth creating a complex condition to temporarily disable smooth scrolling for something that will maybe be used very rarely and it's mildly annoying visually?

I've been looking into how we save and restore the selection when sorting, which is a bit flawed, and I think we should fix this. Once the selection problem is sorted out, it's just a case of temporarily overriding the scroll behaviour of the message list, sorting, and reverting the behaviour change. The behaviour's controlled by CSS, so setting and clearing the override is one line each.

Pushed by sean@thunderbird.net:
https://hg.mozilla.org/comm-central/rev/27f8c6220b21
Scroll instantly when changing the thread tree sort column or direction. r=aleca

Comment on attachment 9342666 [details]
Bug 1838522 - Scroll instantly when changing the thread tree sort column or direction. r=#thunderbird-reviewers

[Triage Comment]
Approved for beta

Thunderbird 116.0b4:
https://hg.mozilla.org/releases/comm-beta/rev/e74bf82d9601

Comment on attachment 9342666 [details]
Bug 1838522 - Scroll instantly when changing the thread tree sort column or direction. r=#thunderbird-reviewers

[Triage Comment]
approved for esr115

Thunderbird 115.0.1:
https://hg.mozilla.org/releases/comm-esr115/rev/61c13595954d