Just to remind everyone that in Firefox 2.0.0.8 (this is a bit out of date but I had only just realised):

The CSS "clear" element is sometimes ignored on pages with elements that use the "float" element. There is a workaround for web developers.

And that workaround is:
JS:

if (window.navigator 
 && window.navigator.userAgent.toString().indexOf('Firefox') != -1 
 && window.navigator.userAgent.toString().indexOf('1.8.1.8') != -1){
 document.getElementById('container').className =
 document.getElementById('container').className + ' clearfix';}

CSS:

.clearfix:after {
    content: "."; 
    display: block; 
    height: 0; 
    clear: both; 
    visibility: hidden;

Though this problem will be fixed in 2.0.0.9.

Just thought everyone would want to know...

Yep it's been fixed I believe - I've downloaded 2.0.0.9 now myself and it's great that Firefox keeps telling you there are new versions so these problems are fixed quite quickly. I noticed this myself when I looked at what Mozilla had fixed in 2.0.0.9