http://www.i3physics.com/blog/2010/07/dsfsdf/
Here is an example.
The part where it said "PHP" (the right top corner) remained as slim as it was. here is part of the css code
.wp_syntax_lang {
background-color:#3c3c3c;
position:absolute;
right:0;
padding:1px 10px 3px;
color:#ddd; font-size:9px; font-weight:800;
text-transform:uppercase;
-moz-border-radius-bottomleft:5px;
-webkit-border-bottom-left-radius:5px;
border-radius-bottomleft:5px;
}
I tried bold, bolder, 700, 800, 900 and is not working under FF.
Its because the font size (9px) is too small to display bold. Try 11px or more and it works fine.