There was a subthread recently complaining about password managers and their UX problems. These aren't aimed specifically at "disabled" users, but I think it's a similar situation. We can't reliably enforce good standards for sign-in (whether that's just setting the autofill attribute correctly and choosing the correct event handlers for Javascript validators or something far more ambitious), so we expect a password manager to just deal with the web as it is. IMHO they work remarkably well given that constraint, but it's not optimal overall.