We should show the search mode indicator without executing a new query when the user cycles through one-offs with the keyboard. We should do this for both Arrowing and Alt+Arrowing through the one-offs. I clarified with UX that as of bug 1657212, Shift+Enter and Alt+Enter on a keyboard-selected one-off will execute a search immediately rather than enter search mode. This is fine, and we should still show the search mode indicator if a key-modifier is being is held down. The rationale is that the action following Enter will be related to the engine named in the search mode indicator regardless of key modifier: we will either enter that engine's search mode if nothing is held down, or perform a search immediately with that engine if a key modifier is held down.

Please see attached drawing. Please also see bug 1657676, which also concerns showing the search mode indicator without executing a new query.

https://hg.mozilla.org/mozilla-central/rev/35e3da7b7672

Backed out from Gecko 82 (beta) for causing bug 1666087:

https://hg.mozilla.org/releases/mozilla-beta/rev/183b951ba5701d5d8ca1fd4184b5a14b3fc74f59

It remains in tree for Gecko 83 (central).

This is actually fixed in Nightly and not worth uplifting.