You might already know, that Safari has a nasty autofill bug where it fills email, username and password fields no matter if you set autocomplete=\"off\" or not
autocomplete=\"off\"
Better than use JS to clear content - simply fake password field:
A password type doubled put the browser in incertitude so it autocompletes only user name
password
fake_pass input should not have name attribute to keep $_POST clean!
fake_pass
input
name
$_POST