Firebug

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Firebug is the most popular and powerful web development tool. There are some qualities of new firebug:-

• Inspect HTML and modify style and layout in real-time
• Use the most advanced JavaScript debugger available for any browser
• Accurately analyze network usage and performance
• Extend Firebug and add features to make Firebug even more powerful
• Get the information you need to get it done with Firebug.

You can use it for editing a webpage. If you want to get your website looks like a professional, then must use it. It can also be used as a hacking tool.