How to personalize web pages with additional functions in Firefox ?

I have many favorite web pages which I visit very often. But not all of them give me the features and functions I expect from them to be perfectly user-friendly. For example: a button in order to download videos from YouTube, the possibility to search Usenet file names from Forums directly in the NZB Index, etc. I would like to make and add my own customizations, but also find some new ideas from an existing community.
1 answer

Scripting with Firefox Addon "GreaseMonkey"

First of all, you must install the Firefox add-on GreaseMonkey from the following link: https://addons.mozilla.org/de/firefox/addon/greasemonkey/. Next, you must restart your PC in order to activate the add-on. On this Page: http://userscripts.org/ , you can find many useful scripts in order to customize and enhance your browser experience. When you have find a script which you are interested in, just click on the install button, confirm the installation and you will find the scripts on the Firefox add-on page. There you can add/remove, activate/deactivate scripts and modify options.
You can find further information’s on how to create and modify scripts on the following Homepage: http://wiki.greasespot.net/Main_Page