It looks simple enough, whatever causes this must be in the CSS. Try not applying the CSS (for example remove the divs), and if then the image void displays with the correct size in FF, you can start hunting down the line that causes this behavior.
By the way I think it's better to use entity codes to display symbols such as the trademark sign, to avoid trans-encoding problems:
HTML Code:
<h1>Webdoken™</h1>
http://htmlhelp.com/reference/html40/entities/