After popup richlist landed, we'll need to define another layout for multi-column popup in autocomplete.xml. We could reference Sean's patch for new multi-column layout.  https://hg.mozilla.org/mozilla-central/diff/3e315a1721ee/toolkit/content/widgets/autocomplete.xml
Hi Ray, I think this item could be independent from other form autofill bugs. You can take it if you have free time for it.
thanks for giving me this good starting point to autofill. I'll soon look into it after work on video control stopped at some points.
Visual spec updated: https://mozilla.invisionapp.com/share/GD8ND99QZ#/screens