Okay, I tracked this down by now, works with HTML5 doctype in FF and chrome now. IE to be tested.
issues:
Chrome: I set css properties using document.getElementById().style.property=.., when using $(..).css() this works fine with html5 doctype
Firefox: Using document.height and document.width did not work, I received NaN. Why ever! using $(document).height() and .width() all is fine.
No clue! about FF issue, maybe someone can tell me.
cheers