When the user is editing the text in the URL bar (typing, backspace, etc.), the first suggestion is always selected.
Because accessibility clients require autocomplete items to be "focused", the code needs to differentiate between explicit selection (e.g. via down/up arrow) and auto selection (e.g. when typing).
Otherwise, the focus continually moves away from the text box while the user is typing, as was previously occurring.
This makes it very difficult for the user to edit text, particularly backspace/delete.
There was a previous attempt to handle this, but it was somewhat fragile and broke completely some time ago.
Now, rather than trying to handle this based on autocomplete events, it is handled in the input and key press events.
For input events, accessibility focus is forced back to the text box and further accessibility focus events are suppressed.
For down arrow, up arrow, etc. key presses, accessibility focus events for suggestions are enabled.
This makes it easier to understand and predict the user experience, rather than relying on underlying autocomplete implementation details.
This is tested using an accessibility browser test, which makes it easier to make assertions about accessibility focus.
This also means that if the underlying implementation details change (e.g. HTML + aria-activedescendant instead of XUL + DOMMenuItemActive events), this test should still be valid and allow us to catch regressions.
Differential Revision: https://phabricator.services.mozilla.com/D5987
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extra : moz-landing-system : lando
