From the top of my head: less animations, no autocorrect on the keyboard, quicker killing of applications, memory pressure events integrated in the built-in applications so they clear out stuff when needed.
More information can be found on the Tarako[1] info page at MDN. I saw the finished device (I have a dev version here with an old build) last week in Oslo and was surprised that it worked that well. Panning the homescreen had no jank and opening and closing apps was fairly fast.