And the ability to be able to Import and Export your bookmarks freely without having to use their website to do so.
(An additional point I should have mentioned last time, I'm speaking about the mobile version, not the desktop version.)
Last time I checked you need to have one of their accounts to export/import bookmarks and stuff. I would be totally glad to be wrong about this though, if I can export all my stuff from DuckDuckGo and import it into Firefox mobile.
Edit: Five minutes after replying I found this article giving hope for the future of Firefox mobile.