This bug is about the states array displayed in the sidebar of the a11y panel.
Some states seem to be updated dynamically correctly in UI (eg enabled) but some are not (focused, readonly).

STRs:

• open a page with an input (data:text/html,<input>)
• inspect a11y properties for the input
• open the list of states
• (notice "autocomplete" is in the list, "readonly" is not)
• open split console
• run document.querySelector("input").setAttribute("readonly", "true")
• (notice that states are not updated at all)
• select another node and select back the input
• (notice that now "readonly" is in the list, and "autocomplete" is gone)

This is also the case for the "focused" state, whenever you focus an element, the state update is not reflected in the UI.

But interestingly if you try to update the "disabled" attribute, then the UI is updated dynamically.

This is problematic for Bug 1702078 where we try to fix the a11y panel initialization, but we get an outdated "focused" state on the initial document.