The Firefox browser is popular because of its user-friendly interface and its variety of features. Add-ons make Firefox quite valuable especially to web designers.  Here  is an enriched suggestion  about a list of the top 10  must-have add-ons you will not give up if you are a web designer:

Firebug - The Firebug add-on is an integrating tool with Firefox. The add-on lets you debug, edit and monitor HTML and Javascript live on any web page.

IE Tab – The Internet Explorer Tab is an excellent tool that web developers use to see how their web pages will be displayed by Internet Explorer. This gives them the opportunity to make any changes or adjustments for users who use this browser.

Pixel Perfect – The Pixel Perfect add-on allows web designers  to overlay a web composition on top of the developed  HTML. It is a Firefox/Firebug extension and integrates  into the applications.

Web Developer – The add-on tool with Web Developer can add a menu and a toolbar to the page with various web developer tools that can be customized for each application.

FireShot – The FireShot add-on application is a Firefox extension that can create portions or full-pagescreenshots of web pages. The FireShot extension is unlike any other plug-in becaus it provides a set of annotation and editing tools that let users modify any web captures, insert text annotations and also any graphical annotations.

Aardvark – Usually, web designers like to clean up their web pages by removing and isolating elements prior to printing them. The Aardvark add-on utility tool is quite user-friendly and integrates well into the applications.

Firecookie – The Firecookie add-on is a Firebug extension that makes it possible to view and manage cookies in the user’s browser. Web developers can maximize this add-on by customizing its features as well.

YSlow – This add-on is used to analyze web pages and report on reasons why they could be slow, based on Yahoo!’s website rules for high performance.

Palette Grabber – Designers who use Photoshop, Paint Shop Pro, GIMP, Flash, Fireworks or Paint.NET can use

 the Palette Grabber add-on to custom-create a color palette in their programs.

GridFox – The GridFox add-on is a Firefox extension that web designers use to overlay a grid on any website. It is very customizable, and the designer can create the exact grid that their layout is designed around.