After reading about it over the last few months, I took the plunge and started using a clever extension for Mozilla Firefox called Greasemonkey, that can be downloaded from http://greasemonkey.mozdev.org/.
After installing it on Firefox, one can download or write user scripts to add features to web pages, making them more usable.
I am using scripts I downloaded that make Gmail more user-friendly by adding "delete" and "mark read" buttons (instead of having to use a dropdown).
I also have a script that allows a form submit by pressing CTRL+ENTER in a textbox, and one that shows Amazon prices in Rand, in addition to Dollars. Another script converts URL text into hyperlinks automatically .
There are apparently also similar similar options for other browsers, but for now, I will stick to Greasemonkey. I have switched between IE and Mozilla/Firefox for the past few years as my default browser, but I finally have a reason to stick with Firefox.
Web developers are going to complain about users being able to mess with their site designs - with good reason - you could make some sites stop working if you install the wrong script - but uninstalling is easy. I would recommend Greasemonkey to experienced web surfers, who are looking for a way to improve their online experience.