Prevent floated divs from wrapping to new line

This should be all you need.

    .float-wrap {
      /* 816 = <number of floats> * (<float width> + 2 * <float border width>) */
      width: 816px;
      border: 1px solid;
      /* causes .float-wrap's height to match its child divs */
      overflow: auto;
    }
    .left-floater {
      width: 100px;
      height: 100px;
      border: 1px solid;
      float: left;
    }
    .outer {
      overflow-x: scroll;
    }
<div class="outer">
  <div class="float-wrap">
    <div class="left-floater">
      One
    </div>
    <div class="left-floater">
      Two
    </div>
    <div class="left-floater">
      Three
    </div>
    <div class="left-floater">
      I should be to the <s>left</s> right of "Three"
    </div>
    <div class="left-floater">
      I float.
    </div>
    <div class="left-floater">
      I float.
    </div>
    <div class="left-floater">
      I float.
    </div>
    <div class="left-floater">
      I float.
    </div>
  </div>
</div>

.float-wrap keeps space open for the divs. Because it will always maintain at least enough space to keep them side-by-side, they'll never need to wrap. .outer provides a scroll bar, and sizes to the width of the window.