If you are a web developer/designer, mozilla add-on can help you to improve your preparing. Here is the add-on from mozilla that I use to create a web page and you should try it :
By colorzilla you can capture the color of a website and then you use it in your applications. Simply by pointing your mouse pointer and click on the desired color, and color codes will tercaptcure automatically.
• Firebug
This addon is a great help to edit, debug, monitor HTML, CSS, Javascript, automatically in your mozilla browser.
By Html Validator, you can immediately see the results of the validation of the web that you have created.
You can measure the width of a column and then you can create an image / banner or determine the width and height of space on your web pages.
Used to see the results of your html code with the user agent in firefox browser.
Add-Ons contain as many user agents Ie, Opera, Netscape, so you can see the results of your website with various user agents.