whitespace above header won't leave. It's fine in safari but not firefox

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White space above header won't leave in firefox. It's fine in safari and IE. I've done no padding and no margin but it still won't work.Everything was fine before I removed my left float from a bottom container.\[code\]body{margin:0 auto;padding:0;}a:link{text-decoration:none;}#heading{ margin:0px auto;font-size:18px;font-weight:lighter;padding:0;background-color:#ffffff ; }#heading ul{ list-style-type: none; float:right; width:600px; margin:0 auto; padding:0;}#heading li{float:right;font-family: "Times New Roman", Times, serif;margin-left:20px;margin-top:25px;margin-right:12px;padding:0;}#heading .ibar{float:left;list-style-type:none;margin-top:25px;padding:0px;}\[/code\]Html code\[code\] <div id = "heading"><nav><ul><li><a href="">Disqus</li><li>Youtube</li><li><a href="http://stackoverflow.com/rss">RSS</li><li>Facebook</li><li>Crunch</li><li><a href="http://stackoverflow.com/ask">Disqus</li><li><a href="http://stackoverflow.com/archive">Twitter</li><li><a href="http://stackoverflow.com/">Home</li></ul></nav><li class = "avatar"><img src="" width="300" height="200" ></li><div class = "clear"></div></div></div>\[/code\]