Greasemonkey is a must have addon for Firefox users,it lets you run scripts that make changes to how your favourite webpages look and behave.There are over 7000 scripts available from http://userscripts.org
You can run as many different ones as you like.The changes are only made locally in your browser,so when you toggle Greasemonkey and it refresh,you see the normal version of the site.
To download Greasemonkey,click here
