I strongly suspect this was a one-time thing due to someone not loading correctly. The password input box is coded to hide the text by default and since an error occurred when you tried to login, I'm confident that this issue isn't permanent. Thank you for posting about it though and if you can reproduce the problem, please let us know!
Firefox 39.0.3. Ubuntu 14.04. Yes, it seems that it was a one time issue, but this one time issue occurred some days ago also (irrespective of the operating system). I would like to add some information: Inside the user name and the password input boxes, there is some text already written and disappears when we click on it (namely "User Name" and "Password"). But at that point of time, I had to manually delete all those characters by the delete key. After that I typed my login details (which were correct but not accepted). Note that the page had loaded completely.