If you have access to all computers that are used then you can lock the pref to remember passwords.This will prevent them from saving any passwords in the Firefox password manager, so if you only want that for that connection and not for other websites then that may not be what you want.
Other methods like using autocomplete=off can easily be bypassed, but if you can’t access those computers and prevent users from removing mozilla.cfg from the Firefox program folder then using autocomplete=”off” is the only method left.
You can use this line in mozilla.cfg to lock the pref signon.rememberSignons
lockPref("signon.rememberSignons",false);
To Know more about mozilla.cfg visit here
