It happens on Firefox whenever you collapse "Content Head7". I'm not sure if this is coincidental to it being the biggest or not. Anyway, The solution was to do this:
.subhold2
{
margin-left:27%;
margin-right:27%;
}
As a side note, that was made much easier by the
Web Developer Extension for Firefox - meant I could find the name of the block I needed, edit the CSS and see the changes instantly.