I’ve tested my page in Chrome, FF and IE8 and all the browser render the text this way:

It is defined like:
font-family: 'Arial', sans-serif;
font-size: 0.75em;
font-weight: bold;
I’ve tried declaring Arial in different ways, using px instead of em and also define the weight in number (600, 800)… But IE9 still renders is “bolder” than the other browsers:

Any help? Thanks
Just to weigh in, you could place a meta tag into your HTML as a quick workaround, which will tell IE9 to emulate IE8, bringing back the original rendering.
To do this, place
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE8" />in your section.However this will come at the expense of other IE9 features you may need, like the better HTML5 and CSS3 support.