I love the new Firefox Home interface and its options to customize it. In my opinion, a really great addition, would be to implement dynamic wallpapers.
By dynamic wallpaper I mean a rotating wallpaper that changes every X time (maybe every hour or a configurable time) so it isn't the same one all the time. I'd say competitors like Chrome already have this option built in.
In Firefox there are extensions that provide this feature but I'd really like it to be standard.