The tab-close-button is not labeled and is missing an interactive role of button, while it is functioning as one.

Note: we do not want this control to be keyboard focusable, because keyboard-only user could close the tab via the context menu and we don't want to create an additional tab stop for the navigation as well, but making sure the control is marked up as a button with an accessible name would allow it to be actionable with speech-to-text software, with touch devices, with switch controls in scan mode, and for screen readers via their navigation shortcuts as well.

The tab-close-button is not labeled and is missing an interactive role of button, while it is functioning as one.

Note: we do not want this control to be keyboard focusable, because keyboard-only user could close the tab via the context menu and we don't want to create an additional tab stop for the navigation as well, but making sure the control is marked up as a button with an accessible name would allow it to be actionable with speech-to-text software, with touch devices, with switch controls in scan mode, and for screen readers via their navigation shortcuts as well.

Backed out for causing bc failures in browser_multiselect_tabs_close.js

• Backout link
• Push with failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | browser/components/tabbrowser/test/browser/tabs/browser_multiselect_tabs_close.js | Close tab button has an expected accessible name with 1 tabs (multi) selected. - {"args":{"tabCount":1},"id":"tabbrowser-close-tabs-button"} deepEqual {"id":"tabbrowser-close-tabs-tooltip","args":{"tabCount":1}} -

Thank you, Cristian! Pushed the fixed test now.

Backed out for causing bc failures in browser_tab_tooltips.js

• Backout link
• Push with failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | browser/components/tabbrowser/test/browser/tabs/browser_tab_tooltips.js | Test timed out -

And probably this one needs work too, not sure yet.
https://treeherder.mozilla.org/jobs?repo=autoland&group_state=expanded&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&searchStr=a11y&revision=a62a8ee7d3c8a06ef6ae6be33edfc2c7c97157d9&selectedTaskRun=Jwybujx2QuiOup8ttrc3hg.0

Oh, sure. I’ll fix it today: thank you for the investigation

removing the hanging NI since there is one of test failures that I do not know yet how to explain and will need a help from someone in Layout team, I think.

So browser_tab_tooltips.js expects that the tooltip element with the id tabbrowser-tab-tooltip will be used for the close button, but that won't be the case anymore with this patch. Instead an anonymous tooltip node will be used. You can get that node like this:

document.addEventListener("popupshowing", event => {
  // event.target is the root node, event.originalTarget is the anonymous tooltip node
});

Does this help?

Here's how I thought browser_tab_tooltips.js should be modified to deal with your changes. So far I've only run it without your changes though (and it passed).

https://hg.mozilla.org/mozilla-central/rev/98f09025ffa6