To display this page, Firefox must send information that will repeat any action (such as a search or order confirmation) that was performed earlier

This happens when you refresh a page that is the result of a POST request (as opposed to a GET request).

To avoid it, you can use the POST/redirect/GET pattern.

Try to change your request type from POST to GET.

If not possible to change the request type, For reloading the page, try using:

window.location=window.location;

Instead of

window.location.reload();

As suggested in answer to the question preventing firefox reload confirmation

Worked very well in Firefox, Chrome..

I had this issue on a website I made. I ended up doing all of the backend work, then using this code:

header("Location: webpage.php", true, 303);

This clears out any post data and redirects the page so reloading will not cause that message anymore.