Just had a little play in firebug
.sidebar {
-moz-background-clip:border;
-moz-background-inline-policy:continuous;
-moz-background-origin

adding;
-moz-border-radius-bottomleft:10px;
-moz-border-radius-bottomright:10px;
-moz-border-radius-topleft:10px;
-moz-border-radius-topright:10px;
background:rgba(58, 88, 128, 0.1) none repeat scroll 0 0;
border:1px solid rgba(58, 88, 128, 0.2);
float:right;
font-size:11px;
margin-top:10px;
max-width:250px;
width:250px;
}
The top block itself it just set with
EWRporta_Portal .topBlocks {
clear:both;
float:none;
width:auto;
}
I think the max-width it's inheriting from the sidebar is what's doing it. If I increase this the block width increases.