When logging and entering username in the input field you get the auto complete option for your username, pressing down (to select your email with the auto complete) and hitting enter moves focus to the password field rather than letting the browser perform the auto complete.
This is due to line 139 - 143 in https://s3.amazonaws.com/nxcache/account/js/login.js
Replicated in Firefox on Windows, its fine on Chrome though.
$('#login-input-username').keypress(function(e) {
if(e.which == 13) {
$('#login-input-password').focus();
}
});
Wrap the focus in a 0ms timeout to push it to the end of the execution stack, should fix it!
If you extend the maintence anymore I am just gonna keep finding bugs for you guys!