Interesting issue reported by a user: if you have empty p tags in your annotations, then a self-closing div is output to the HTML. If you then open the file in Firefox, it will screw up, but if you give the file an .xhtml extension, it works fine.
I should put in a trap for empty paragraphs, and insert a non-breaking space into them. That could easily be done in the XSLT. Making this a task.