I'm running the control in a DotNetNuke website (localhost, IIS7, Win2008ServerR2), running it from whithin an ascx web user control. Basically I only got the default basic code. 1 FileUpload / 1 progressbar not inline.
I got a trigger on the progressbar from a submit button and when I click it, the progress.aspx shows up and things run pretty smoothly ... in IE7 that is. Trying the same thing in FireFox results in a much less desirable result.
With small files I get the popup, it then refreshes and shows a blank bar and then when it finishes it shows the completed bar, then refreshes again and closes. With a larger file, the whole browser hangs until it finishes and the blank progress bar stays and popup doesn't close.
I tried this using the demo code as well (ASP.Net Dev Server from VS debug) and I get pretty much the same behavior. Works in IE, not in FF.
Basically, something's gotta be wrong with the FireFox implementation or I'm missing something.
I just tested the Demo.aspx page in asp.net dev webserver with FF 3.6.2 and it works fine for me. Does upgrading FF from 3.6 to 3.6.2 help? How about disabling Firefox extensions/plugins? Can you reproduce the problem from another client machine?