I've decided to go with the Atom format for syndication of data in the web application I develop at work. Inside the content tags, I'm placing inline XHTML (not escaped). I then wanted to use an XSLT to show the feed more nicely in the browser. Simply using <xsl:copy-of select="atom:content"> worked for Internet Explorer, but not for Mozilla Firefox. It turns out it wasn't treating the content as XHTML, so I wrapped the content inside a div: <div xmlns="http://www.w3.org/1999/xhtml">