I've spent a good amount of time today trying to work out this surprise issue. Ironically I got a new macbook pro this weekend...and boy it sure came in handy for a reason I did not anticipate.
File upload is stupendously broken in Flash, on all browsers, on OS X Leopard. As details come out I'll see what I can learn here. We have been searching for potential fixes here today, for some of our applications depend heavily on this feature.
Darren J. McNally, Technical Support Engineer, Adobe Flash/Flash Player Support
My first thought is that while its nice that they're going to fix it, I think this needs to be addressed now. I mean, like, right now. Big companies are going to lose money on this. People expect consistent functionality, and this is a real showstopper bug on a big feature.
So far I've looked at the headers being sent by Firefox and Safari to see if there is any useful information:
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:18.104.22.168) Gecko/20071008 Firefox/22.214.171.124
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us) AppleWebKit/523.10.3 (KHTML, like Gecko) Version/3.0.4 Safari/523.10
So as you can see, we can tell....that we're on a Mac. Of some sort. Not very positive so far. Hopefully some more useful information should follow.