I had a look and it was already checked for me.
Bug 1610341 Comment 6 Edit History
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I had a look and it was already checked for me. (Should I renew the ni? ?)
~I had a look and it was already checked for me. (Should I renew the ni? ?)~ I was wrong. I tested on two different machines. The one I tested earlier today with, had "the 'keyboard navigation' related checkbox at the bottom" not checked, just as Neil suggested. Turning it on makes Firefox behave similar to Chrome.