Typography: H3 different sizes in IE 8 or FFox8

I noticed a big difference between Font Sizes using IE-8 or FFox-8

look at the sample images attached to see how the appear in each browser...

Can we do anything in layout.CC or template_css.css to minimize this big differences?

then add implicit definitions like this to the bottom of template_css.css:

h1{
font-size:18px;
}

h2{
font-size:16px;
}

h3{
font-size:14px;
}

....