Greasemonkey has always been one of the most powerful plugins for Firefox and Flock.  Although I mostly used it to make my Myspace experience a lot more pleasant, I've recently decided to start collecting Greasemonkey Scripts again.  Wow.  There are some real timesavers in here.  I've recently used it to supercharge my Gmail with scripts that will change the layout to something more visually appealing, add a "feeds" button that intergates with Google Reader, and even a collapsable feed box that is viewed alongside my regular mail.  Oh, and adding feeds to Google Reader is really easy with the Smart Google Reader Subscribe Button.  Also, a lot of people don't know that Google reader does import and export OPML files so it is really easy to make the transition from your current feed reader.  There is a lot more I'm doing with it of course having mostly to due with shortcuts, events, etc, but I'll get to that some other time.By the way, if you notice me blogging a lot more, it's because I've recently been using the Scribefire extension for Flock and Firefox.  It's prettty badass.  It even allow you to blog to Myspace pretty easily with an addon.