adding to what ralph said:
display:inline-block; or overflow:hidden; will also do nicely.
ANOTHER TRICK:
#company-info, #company-addy{
display: inline-block;
text-align: left;
font-size: 200%;
}
#masthead:after{ content:'';
display: inline-block;
width: 90%;
height:0;
}
#masthead{ text-align: justify;}
this doesn’t require clear fixes and will collapse more naturally ( even without media queries)
hope that helps