Line 1387 in beta 2:

div.innerHTML = ' <link/><table></table><a href="/a" style="color:red;float:left;opacity:.5;">a</a><select><option>text</option></select><object><param></object>';

This is invalid xhtml, the param parameter is not closed. In Firefox 3, on an xhtml page, this results in:

Error: mismatched tag. Expected: </param>.

Source File:

Line: 1, Column: 182

Source Code:

<div xmlns="http://www.w3.org/1999/xhtml"> <link/><table></table><a href="/a" style="color:red;float:left;opacity:.5;">a><select><option>text</option></select><object><param></object>

Fix is easy, close the tag.