GM object not available in firefox debugger console

Question

Unable to get access to the GM object in the Firefox debugger console.

// ==UserScript==
// @name     test_script
// @version  1
// @grant    none
// @include  *
// ==/UserScript==

document.GM = GM; // The GM object can not be accessed using document.GM in the developer console 
console.log(GM): // This works and the GM object contains GM.info object as expected