What link were you using from Subeta?
I upload directly from Subeta with this URL:
http://avatar.subeta.net/slib/avatar.php/475633.png(You would need to change the user ID to your own, of course.) I usually have to wait a bit, though, for the link to update to whatever HA I'd recently changed into that I wanted to upload. I also use Firefox, and I've never had a problem with uploading this way.
I'm also not sure when you attempted to upload, but I did hear earlier that some users were having wardrobe issues earlier on Subeta. So the issue might have been with Subeta, and you just had unfortunate timing when you were playing in your wardrobe and attempting to upload.