FireBug

I definitely saved the best for last with this extension. FireBug is one of the premier debugging tools for Ajax, JavaScript, CSS, and XHTML applications. It supports error and warning descriptions for JavaScript and CSS. This tool not only provides extremely accurate feedback about errors—such as what went wrong, what line it happened on, and what file it happened in—it also opens the file within the Debugger tab and highlights the line of code that is throwing the error. Now that is accuracy! But it gets even better: Not only does it provide the error, it allows us to set breakpoints in the code from the Debugger panel and rerun the page to stop the page when that line of code is reached. I never dreamed of such things with JavaScript! ...

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