Question

When I use firebug and hover over the parent box nothing is shown. I would have expected it to highlight the 3 sub boxes (because they are the children).

When I remove the float right from the sub boxes it works fine.

<div class="parentbox">
    <div class="subbox">box1</div>
    <div class="subbox">box2</div>
    <div class="subbox">box3</div>
</div>  

.parentbox
{

}

.subbox
{
     margin-right:10px;
     font-size:50px;
     float:left;
}

Answer 1

try:

.parentbox
{
   overflow:auto;
}

FYI: Firebug won’t highlight the child elements, just the element you are focussing on.

A better way to do the above would be:

<div class="parentbox">
    <div class="subbox">box1</div>
    <div class="subbox">box2</div>
    <div class="subbox">box3</div>
    <div style="clear:left;"></div>
</div>  

See http://jsfiddle.net/3f22H/ for a comparison – they both have similar end results.