Estou procurando um complemento para poder configurar regras
DOMAIN="*testdomain.com*"
CSS_to_add=".addblockermessage { display: none;}"
Greasemonkey é perfeito para isso.
About this Add-on
Allows you to customize the way a web page displays or behaves, by using small bits of JavaScript.
You can write your own scripts, too. Check out http://wiki.greasespot.net/ to get started. Many scripts already exist, probably ones to enhance your favorite sites. Find them at http://wiki.greasespot.net/User_Script_Hosting .
Fonte Greasemonkey