This issue occurred suddenly. Till yesterday everything was fine. Today when I click on the "Add an Image" icon from post-new.php page and click on "Choose file to upload" button, nothing happens. It works fine in IE7, but there, the overlay box is aligned to the bottom and hence even if the file is being uploaded, I cannot get the "insert to post" button.
I use the latest FF version and I have cleared my cache, cookies and all. Can someone please please help? I really need this fixed.