I am also having problems, though not the same as any I've seen in the forums yet. While using the uploader I can browse to the file and select it, but then the flash window turns into a login screen.
Even though the window is messed up, it shows 1 image in the gallery. However, when you click on the gallery tab, nothing is there.
I've updated all my plugins, disabled all my plugins, had the site open without other tabs running, downloaded and installed the latest version of Flash, cleared the cache, restarted Firefox, rebooted the PC, and ran in a circle until I fell down and threw up. I might have done something else that was suggested elsewhere, but I can't remember on account of how dizzy I am.
Anybody have any clue?