hit regions Firefox support update

Hi. Here's an update of hit region implementation in Firefox in case if
you're curious .

This week we've got a prototype of hit regions which can be used to change
accessible boundaries. The work hasn't been landed into Firefox Nightly yet
but there's a try build [2].

There's no plans to continue the work on drawFocusIfNeeded to fit it for
accessible boundaries setting since hit regions looks promising. It's worth
to notice though that drawFocusIfNeeded (used to draw the focus) is part of
Firefox and there's no actions to undo this.

You can follow hit regions work by watching Mozilla bug [1].

Thanks.
Alexander.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=966591
[2] https://tbpl.mozilla.org/?tree=Try&rev=a0775f0bf042