Login to Pownce via http://www.pownce.com/. Allow Firefox to save your login information for next time, and then log out.
Navigate to http://www.pownce.com/ and type the first part of your username in the “Enter username…” box. Firefox will supply all of the matching usernames it remembers for this site. (So far, so good.)
Select your username and press return to have the browser autofill the rest of your information. Oh look, there’s your Pownce password in plain view! I hope no one in the room was watching you login…
The method that Pownce is using to show the “Enter password…” prompt in the password field is the reason for this malfunction; browsers force all text in password fields to be hidden with asterisks, so if you want to show normal text in a password field like Pownce has chosen to, you have to do so in a non-standard way.