thoron

Here’s what’s going on: When you make a footnote inside a paragraph, the output is basically:

<p>Some <div>Footnote content</div><script>/* ... */</script> text.</p>

Now, HTML5 doesn’t allow a <div> element inside a <p> element, so browsers parse it as:

<p>Some </p>
<div>Footnote content</div>
<script>/* ... */</script>
text.

Replacing the <div> with a <span> seems to work with no troubles, at least on Firefox. (With absolute positioning, inline and block-level elements behave the same way.)