with inject mode instant history.length is 1 more than it actually is

[Owyn]

I have noticed my script can no longer detect when there is no back histry button on the page and it turned out that history.length returns 2 for userscripts when from browser console it returns 1 if the inject mode setting is turned to instant and the sandbox is JavaScript and the run at is document-start

example script:

// ==UserScript==
// @name         New Userscript
// @namespace    http://tampermonkey.net/
// @version      2025-02-28
// @description  try to take over the world!
// @author       You
// @match        https://*/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=github.com
// @grant        none
// @sandbox		JavaScript
// @run-at		document-start
// ==/UserScript==

(function() {
    'use strict';

    // Your code here...
    console.error("history length: " + history.length);
})();

result:

TM: 5.3.3
FireFox: 135.0.1 (64-bit)
Win: 10