version 2.50 if I read it right.
I can not say how much is modified as I do not know what there original looks like.
I believe most of our coding is externally done in say like flashupload.php however if there newer files change function names or things work differnet you will have issues trying to just update the swfupload.
js etc
That would explain your issue and why no one has reported an issue your using a MAC.