What is wrong with this HTML5 <address> element?

Question

<div id="header-container">
      <address>
        <ul>
            <li>lorem ipsum</li>
            <li>(xxx) xxx-xxxx</li>
        </ul>
    </address>
</div>

And the CSS looks like this:

#header-container address {float: right; margin-top: 25px;}

When I load the page, it looks fine in Chrome & IE, but in Firefox it's ignoring the styling completely. When I view source in firefox it looks like above, but in Firebug it looks like this:

<div id="header-container">
    <address> </address>
    <ul>
         <li>lorem ipsum</li>
         <li>(xxx) xxx-xxxx</li>
    </ul>
</div>

Answer 1

HTML5 is still a draft. Firefox 3.6 doesn't completely support HTML5 yet.

And according to the HTML4 spec, address can only contain inline elements:

<!ELEMENT ADDRESS - - (%inline;)* -- information on author -->
<!ATTLIST ADDRESS
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

This is why Firefox considers it invalid and your page breaks.