Okay, I have zero experience in writing javascript, so what I have is basically copypasted from other sources.

I'm trying to make a window close immediately after opening a specific site (in this case, tumblr.com).

// ==UserScript==
// @name           726366
// @description    Closes tab immediately after opening tumblr.
// @include        http://*.tumblr.com*
// ==/UserScript==
Nothing happens. I have also tried window.close();