From bug 1774174 comment 7

Steps to reproduce with Orca:

1. Navigate to the addressbook table and add two rows.
2. Focus the second address input.
3. Insert+A to switch to browse mode.
4. Shift+Alt+ArrowRight. Moves to the checkbox, and announces row and column.
5. Shift+Alt+ArrowUp. Moves to the checkbox on the first row, and announces row and column.
6. Shift+Alt+ArrowLeft. Moves focus to email address input, and announces row and column.
7. Shift+Alt+ArrowLeft. Moves focus to the selector, and announces row and column.
8. Shift+Alt+ArrowRight. Does nothing!

Basically, as soon as you get to the first column, you get trapped there. I tracked it down, and, ironically, it is caused by the screen-reader-only rule:

position: absolute;

https://searchfox.org/comm-central/rev/299e3791e29995873d344ab0d6ac2202ebba93f6/mail/themes/shared/mail/vcard.css#246

Removing the line gets it to work. I think it may have to do with the fact that browse mode takes the screen position of elements into account, and the lack of a position may be throwing it off. Not sure if this would be considered a bug with Orca.

We move the screen-reader-only class to a contained <span> element instead. Thus the <span> has position: absolute applied to it instead of the <th>, but the <th> still has the required text content.

Pushed by nicolai@thunderbird.net:
https://hg.mozilla.org/comm-central/rev/1c38fde68b4b
Avoid screen-reader-only class on <th> elements in addressbook email table. r=aleca

Comment on attachment 9283015 [details]
Bug 1776644 - Avoid screen-reader-only class on <th> elements in addressbook email table. r=aleca

[Approval Request Comment]
Regression caused by (bug #):
User impact if declined: Broken table navigation when using Orca
Testing completed (on c-c, etc.): Tested manually with Orca
Risk to taking this patch (and alternatives if risky): Low. Minor change to the markup.

Comment on attachment 9283015 [details]
Bug 1776644 - Avoid screen-reader-only class on <th> elements in addressbook email table. r=aleca

[Approval Request Comment]
Regression caused by (bug #):
User impact if declined: Broken table navigation when using Orca
Testing completed (on c-c, etc.): Tested manually with Orca
Risk to taking this patch (and alternatives if risky): Low. Minor change to the markup.

Comment on attachment 9283015 [details]
Bug 1776644 - Avoid screen-reader-only class on <th> elements in addressbook email table. r=aleca

[Triage Comment]
Approved for beta

Thunderbird 103.0b2:
https://hg.mozilla.org/releases/comm-beta/rev/8d8173580e1b

optimistically approving for TB102.0.1 - assuming it will pass beta over the next several days

Thunderbird 102.0.1:
https://hg.mozilla.org/releases/comm-esr102/rev/d9ef0d2336c0

Comment on attachment 9283015 [details]
Bug 1776644 - Avoid screen-reader-only class on <th> elements in addressbook email table. r=aleca

[Triage Comment]
Included in 102.0.1.