GM 0.9.2
FF 3.6.16 on XP
You can replicate this by just using this script and looking at the
menu item order:
// ==UserScript==
// @name testscript
// @include *
// ==/UserScript==
GM_registerMenuCommand('one', function(){});
GM_registerMenuCommand('two', function(){});
GM_registerMenuCommand('three', function(){});