This fixes a quite severe user experience issue where pressing the
'alt', 'meta' and/or 'ctrl' key along with one of the supported keys
(e.g. 'f' to enter video fullscreen mode) would overwrite the default
browser behavior. In the case of 'f+meta' we would enter fullscreen
mode, and not open the browser search panel as one might expect.
This change is required to stay consistent with the way YouTube
handles keydown events.
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