Firefox on Windows: If you've always wanted to modify websites with Stylish and/or Greasemonkey but lack the CSS or JavaScript chops, Customize Your Web lets non-developers change the appearance of web pages and add functionality to them.
Using Customize Your Web's WYSIWYG editor, you can change the appearance of elements, hide them, or copy and paste them somewhere else in the page. You can also add keyboard navigation or auto-executing macros. For advanced users, Customize Your Web also supports inserting HTML and JavaScript. Check out the demonstration video above for an overview of what Customize Your Web can do.
If the interface to Customize Your Web looks daunting at first, start off with the extensive documentation on the project's wiki.
If you've tried Customize Your Web to bend the web to your will, share your thoughts in the comments. Customize Your Web is a free Firefox extension, Windows only.
Customize Your Web [Mozilla Add-ons]