In fact, most seem to pertain to IE9 Beta 1.
Changelog is here:
My internal tests show some sort of performance gain of approximately 7.45% (it's not much, but at least it's something) - though this is not important.
Whilst on the subject - will it be safe for us to update TinyMCE on our forums, or should we wait for XenForo to release a build with an updated TinyMCE include?
I also assume SWFUpload has been customised?