Firebug is complaining about a error in
<!DOCTYPE html>, but the HTML source is passing without problems the HTML W3C validator.
Do you have any idea? Sorry, I can't share the source code.
So the following HTML was added in the footer of the page:
At some point I renamed the file slider.js, so it stopped being loaded, and this is the reason behind the Firebug error.
In the "Net" tab, Firebug was not showing any error; it was showing just a "301 Moved Permanently" next to the slider.js file.
Maybe this is your Problem, too: http://blog.rki-home.de/2008/10/22/firebug-syntax-error-und-doctype/ It's german so here what it says in short:
When FireBug states an error, i would think it's always an JS-Error. So FB tries to parse html as js.