I am only able to view the JavaScript files of the website via the Script panel. How can I edit it? I tried everything like double clicking the line that i want to
(source: fidelitydesign.net)
You can use the Firebug Console tab to write Javascript. I use this quite a lot of rapid prototyping of code before I integrate it into my projects. When you use the Console, javascript is executed in the context of the current page. Therefore, and scripts that are currently defined for that page, can potentionally be redefind. E.g., in the Console window, I could do this:
$ = function() { alert("Whoops"); }
...and that would redefine the $ function used by JQuery.