Bug 916383 - Invisible autocomplete items selectable by keyboard when 'your results' not shown

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extra : rebase_source : dc9ffd9026b5060d9606140ccfcc77de1ff972aa
Bug 891667 - Define and implement keyboard interaction with half-height autocomplete.

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extra : rebase_source : b79131c2937a3c64db3a7b2dbf7940df9fc8e45d