View Source Chart
Yet another useful add-on, View Source Chart can be downloaded from the Firefox Extension Library much like Firebug. This extension takes code and displays it in a colorful, graphical fashion that allows you to see the extent of select pieces of code: where they begin and end and what other pieces of code they have an effect on within any given page. By representing each piece of code with a different color and indentation, it becomes much easier to isolate and locate specific errors within your JS or HTML coding. With other features included such as the ability to zoom into complex parented code, it remains to be seen if another extension can outperform this little gem.
It is also helpful to use Pingler’s Browser Details Tool to quickly determine the specifications of your machine and browser. By knowing all of the browser details, you can determine whether or not the error you are seeing is due to coding or simply to do with a particular version of an internet browser.