Hi Ralf,
Form autocompletes are mostly controlled by the browser, there was another user some time ago that also had this issue I think: AIRLINE, FLIGHT No DROPDOWNS
Mine still work in Chrome and Edge, and still do not work in Firefox. So it seems like little has changed since the previous post. For Firefox, the only other thing I found is maybe check the settings described here to see if they are disabled: Control whether Firefox automatically fills in forms | Firefox Help
Best regards,