Hmm there's no reason why that would cause the contents to not appear in Firefox. I just tried your code snippet above inside the default demo, and it shows up fine. Make sure the paths to the images in your snippet is correct; if in doubt use absolute URLs to them:
Code:
<ul id="adverts">
<li><img src="http://mysite.com/images/Quarter-Page.png" alt="Quarter page advert 9.35cm high x 6.65cm wide" border="0px">9.35cm high x 6.65cm wide</li>
<li><img src="http://mysite.com/images/Half-Page-Portrait.png" alt="Half page portrait advert 19.2cm high x 6.65cm wide" border="0px">19.2cm high x 6.65cm wide</li>
</ul>
Bookmarks