The value of the NavigatorID.product property is always "Gecko", in any browser.
productName = window.navigator.product
The string "Gecko".
<script>
function prod() { 
  dt = document.getElementById('d'); 
  dt.innerHTML = window.navigator.product; 
}
</script> 
<button onclick="prod();">product</button> 
<div id="d"> </div> 
<!-- returns "Gecko" -->
 | Specification | Status | Comment | 
|---|---|---|
| HTML Living Standard The definition of 'NavigatorID.product' in that specification.  |  Living Standard | Initial definition | 
| Desktop | ||||||
|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
| Basic support | Yes | Yes | Yes | Yes | Yes | Yes | 
| Mobile | |||||||
|---|---|---|---|---|---|---|---|
| Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | iOS Safari | Samsung Internet | |
| Basic support | Yes | Yes | Yes | Yes | Yes | Yes | ? | 
    © 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
    https://developer.mozilla.org/en-US/docs/Web/API/navigatorID/product