This code now needs to get merged into the browser so it can access elements within the application. We do this by providing a [http://developer.mozilla.org/en/docs/XUL_Overlays XUL Overlay] file. A XUL Overlay is a .xul file that specifies XUL fragments to insert at specific merge points within a "master" document. Often this is used to add new UI to an application (e.g., a new menu item), but in our case we'll use it to merge our addtabbeside.js script into the browser.

<pre>

<overlay id="addtabbeside-overlay"

xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">