KeyboardEvent.key value "Left" is obsolete and will be renamed to "ArrowLeft

KeyboardEvent.key value "Left" is obsolete and will be renamed to "ArrowLeft

Hi,

Firebug is reporting the following warnings after the right or left arrow keys are depressed:

KeyboardEvent.key value "Right" is obsolete and will be renamed to "ArrowRight". For more help https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent.key
event[ prop ] = originalEvent[ prop ];
jquery.js (line 4564)

KeyboardEvent.key value "Left" is obsolete and will be renamed to "ArrowLeft". For more help https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent.key
event[ prop ] = originalEvent[ prop ];
jquery.js (line 4564)

The line numbers are in jQuery 2.1.3 full source.

All appears to be working OK, however.

The web page is a photo gallery using Slimbox.  Neither jQuery nor Slimbox contains the string "KeyboardEvent".  Is this a jQuery internal problem or what?  Just what is going on here?

JPL