If you're posting from the Wincustomize forum, click the My Account button above and you should be able to upload the following size ...

I am using firefox, and it does not work. In fact, most of my problems with this website are when I use firefox. (Aanother example is the "forums" bottom tshat does not show correctly and makes it unclickable, which is another bug that appears on some firefox browsers).

I'll try with exploder this afternoon.

I use FF and the avatar uploaded fine for me. But on occasion i do have trouble posting.

Another thought i had was to make sure that you have peer block off, if you use it.