If the Megabar is unfocused and a new tab is opened, we focus and expand the Megabar in the new tab. However, if the Megabar is in its Focused & Collapsed state and we open a new tab, it remains Focused & Collapsed. This isn't right. We should always expand the Megabar when a new tab is opened.

What content is going to be present in the expanded new-tab state when there is no user input?

While Safari does this on click (see Bug 1558000), I can think of no other browser that automatically expands the addressbar with spurious suggestions when the user has shown no intent for suggestions in that area -- this would serve to weaken the value of new tab (either built in or add-ons).

I just tested what happens if I type a query and delete it in the megabar -- it collapses, so it feels to me that Firefox before this bug doesn't have a real suggestion for me.

By expansion, I mean displaying Megabar's larger input. There won't be any autocomplete results on a fresh tab before the user interacts with the Urlbar.

Got it -- I see what you mean in new tabs after an original new tab where the user collapses the focus (border). Thanks for clarifying!

https://hg.mozilla.org/mozilla-central/rev/676e5ab47942