After looking at your CSS, I believe the only issue is that you don't appear to be defining how the newer HTML5 elements should be displayed. It's common to sim

After looking at your CSS, I believe the only issue is that you don't appear to be defining how the newer HTML5 elements should be displayed. It's common to simply put display: block, or inline-block, for all of the HTML5 element that you're using. This should fix the garbled mess that you see in the screenshot. I don't believe that there is much more to it than that. Although, I do not have the version of Firefox mentioned to test on.