If you don't have Greasemonkey, you can get it here for Firefox. To use this script, press Alt + T + G + N (one after another) and then type whatever you want in the spaces (it doesn't matter, everything will be changed in the next step), then press OK.
It will open Notepad, delete all of the text and then copy/paste this:
// ==UserScript==Save and close the file. Refresh the page, and you should find a link to the groups page right here:
// @name Stickpage Custom Forums link
// @namespace spgroups
// @description Puts a link to the "Custom Forums" a.k.a. groups on the front page.
// @include http://forums.stickpage.*/*
// ==/UserScript==
var allNav, thread, indicator, groups;
allNav = document.getElementsByClassName('breadcrumb');
nav = allNav[allNav.length - 1];
groupsText = 'http://forums.stickpage.com/group.php?cat=1">Custom Forums';
groups = document.createElement("div");
groups.setAttribute("class","navbarlink");
groups.innerHTML = groupsText;
nav.parentNode.insertBefore(groups, nav.nextSibling);

Enjoy.
If there are any problems, post them here.