Extensiones de Firefox útiles para el diseño web

Web Developer 1.1.9: The Web Developer extension adds various web developer tools to a browser. https://addons.mozilla.org/es-ES/firefox/addon/web-developer/

ColorZilla: Advanced Eyedropper, ColorPicker, Gradient Generator and other colorful goodies...   https://addons.mozilla.org/en-US/firefox/addon/colorzilla/

Firebug: Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page... https://addons.mozilla.org/en-US/firefox/addon/firebug/

Measurelt: Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels. https://addons.mozilla.org/en-US/firefox/addon/measureit/