real time css editor
another great mozilla firebird extension : EditCSS
from the author:
EditCSS is a useful extension for web developers and web designers, that works for MozillaFirebird. It allows you to edit current stylesheets of a page in live, and display the result as you type. It appears in a sidebar. The project is based on Jesse Ruderman's "Edit Style" bookmarklet, that has done the essential work.