Dear @Thunderbird ,
I know you are changing for the better. However while testing Thunderbird 111 daily I would like to see some gradual improvements so it becomes ready for most userf of Thunderbird 115 in terms of #screenreader #accessibility once it's declared stable.

Positive things I have noticed:

We have brand new message list that no longer renders all the messages in selected folder at once but only those that are visible on the screen and ready for the user interaction. From my point of view it looks similar to infinite lists on mobile platforms. Most importantly it almost fully elliminates enormous lag when browsing huge message lists on linux with #orca #screenreader running. I was curious enough and I have tested imap folder with up to 75000 messages inside.

It is still possible to use F6 and shift+F6 to move the keyboard focus from the folder tree to the message list and back.

Message list has headers that are used for sorting and a popup menu for setting up visible columns almost from the begining of Thunderbird existence. From now on these controls are finally accessible to screenreader users. And we are now able to configure sorting and show / hide individual columns.

We can still use ctrl+shift+k to show / hide the filter entry. Also there are accessible buttons alongside the filter entry that allow quick filtering the list such as labelled messages, messages with attachments, starred messages, messages from addressbook contacts, unread messages, even ability to keep the filter active when changing folders. Some of these features were already there earlier but now these are accessible to keyboard users including screenreader users.

Now features that need some polishing:

It appears we can now open individual message folders on a new tab / in a new window however this feature needs some fixes. For example when navigating using up and down arrow keys in the folder tree, pressing shift+F10 first moves focus to the parent folder and displays popup menu for that parent item instead of currently selected one.

When navigating in huge list new selection is not properly reported to assistive technologies while scrolling. For example press end to move to the last message. Now press up arrow key several times to navigate back a message and notice how screenreader is reporting new selection as it happens. Now press the page up key to move the selection by the larger increment. New message is highlighted but the selection changed event is not fired properly or it's getting mixed with some spurious focus event on an unlabelled pannel. Some screen readers are able to filter out these but I think it would be nice to address it at the source rather than working it around.

Now the main window has a lot of focusable controls and it is no longer comfortable to use tab and shift+tab to navigate. It would be nice if buttons were grouped in a toolbar like controls implementing toolbar pattern the way it's explained at
w3.org/WAI/ARIA/apg/patterns/t…

It's nice that ability to reconfigure message list columns is now fully accessible to keyboard and screen reader users however accessible name of each item in the message list does not yet respect these settings. Subject is the only content that is communicated to assistive tools when navigating in the list using arrow keys. This is major issue and will likely be considered as a regression if it won't be addressed before releasing the stable version.

When navigating in the list of messages it is possible to select multiple messages for executing actions on them. I am afraid the fact multiple messages are selected or not selected is not properly communicated to assistive tools. This is major issue for screenreader users.

It is no longer possible to use applications key / shift+f10 to inwoke a popup menu in the message list.