One of the huge advantages of Mozilla FireFox , as compared to other browsers, it was, it still is, to possess a large amount of free extensions that allow you to customize and extend the application. As a web developer I can not - now - without it some useful extensions that help me in the construction, inspection and maintenance of Web pages
A "must" for all Web developers is probably the most advanced editing and real-time debugging of Web pages on the Internet today. Certainly exceeds in usability and functionality (as well as in Plugins and extensions available) also control tools supplied with WebKit (see Safari and Chrome) and the new Explorer 8.
This extension I discovered recently and I was really amazed at the precision and ease of use. It allows you to perform a series of checks on the syntax of the pages so as to blow out errors markup tags or misused or not closed. Convenient especially to those developed with WordPress or similar systems, where a page is built with various parts (header, body, footer and sidebar) difficult to examine and display as one.
Note: This extension is indicated on the repository as Mozilla NOT available for MacOS systems. However, if you go to the page developer , you find all versions instead. In fact, I use it safely on my Mac!
Manufactured by Yahoo, YSlow is an add-on FireBug and allows for extremely advanced in the pages of the report that we are developing! With lots of votes! From the analysis it is possible to obtain a series of suggestions - often very useful - to improve the stability and performance of our web pages
This extension is present both as an add-on FireBug, both as a stand-alone extension for FireFox. They are also developing versions in Adobe AIR and Adobe Dreamweaver. Code Burner provides a contextual Help - evolved - the HTML markup and CSS, indicating the cross-browser compatibility, general information, syntax, and another example: