Question: I'm working on a Firefox extension and I need to inject a JavaScript into a page from a content script. In my Chrome extension I have done the following:

```
this.initializeJplayerSupport = function() {
  var script = document.createElement('script');
  script.setAttribute('type', 'application/javascript');
  script.setAttribute('src', chrome.extension.getURL('js/custom-jplayer.js'));
  document.head.appendChild(script);
}

```

The file is in my data directory. How can I reference a js file in a firefox extension content script (where I have used `chrome.extension.getURL()` for Chrome)?

Answer: 
If you're in main.js in your SDK-based add-on, you require and use the 'data' helper from the 'self' object:

```
var data = require('self').data;

console.log(data.url('somefile.js')); // prints the resource uri to the file.

```

For more info: 

<https://developer.mozilla.org/en-US/Add-ons/SDK/High-Level_APIs/self#data>

Once you get this resource uri, you can then supply it to a content script using self.postMessage or self.port.emit:

<https://developer.mozilla.org/en-US/Add-ons/SDK/Guides/Content_Scripts>
It looks like that starting in Firefox 38, `cfx` has been replaced with `jpm`. 

Which might be why this line wasn't working for me:

```
var data = require('self').data;

```

I simply had to rewrite it a bit:

```
var data = require('sdk/self').data;

```