Convert simple chrome extension to firefox addon

I have a simple chrome extension, which consists basically of a manifest file and one tiny js file with one function. The function is called like this: [login to view URL]("beforeload", MyFunctionName, true); The purpose of the function is to attach on beforeload event on all html tags within the currently loading webpage, including <script> tags. If the current tag to be loaded is <script> and has 'src' attribute, the function suppress (disables) downloading of the given src script file at all - if the URL matches hardcoded regex. I need to convert this to FireFox addon, to make the function execute the similar way when a webpage is loading in firefox.