Yes it can- that's the first thing I tried- but it will not iterate forever. The trick is to use indirect recursion:

  <div id="a"></div>
  <div id="b"></div>

  #a,
  #b {
    height: 200px;
    width: 200px;
    border: dashed;
  }
  #a {
    background: -moz-element(#b) no-repeat;
    background-size: 80%;
    border-color: green;
  }
  #b {
    background: -moz-element(#a) no-repeat;
    background-size: 80%;
    border-color: purple;
  }

With Firefox and CSS background you can open a portal to another dimension

That's the same thing I immediately had to try as well :)

The argument of -moz-element() can be a child of the styled element, but it can't be a parent (makes sense).