Nit: align the properties on subsequent lines with the reference on the first one, i.e.:

```
  let origin = shell.contentBrowser.
               contentWindow.wrappedJSObject.
               WindowManager.getCurrentDisplayedApp().origin;
```

Although in this case you have enough horizontal columns to shorten this to two lines:

```
  let origin = shell.contentBrowser.contentWindow.wrappedJSObject.
               WindowManager.getCurrentDisplayedApp().origin;
```