Have you ever heard the phrase “Yo dawg we heard you like…”?

It introduces the concept of recursion, in that you can put something inside another of itself, and use both objects simultaneously.

For example:

Yo dawg, I heard you like pizza, so I put a pizza inside of your pizza so you can eat pizza while eating pizza!

Or how about the classic:

Yo dawg, I herd yo and yo dawg like yo-yos so we put yo dawg in a yo-yo so yo can yo-yo yo dawg while yo dawg yo-yos, dawg

Did you know that this applies to the Mozilla Firefox web browser as well? You can actually load a Firefox window inside of another Firefox window!

Here’s how you do it:

1. Open Firefox, if you aren’t using it already (shame on you).
2. Visit chrome://browser/content/browser.xul in the address bar
3. And behold the glory of Firefox inside Firefox!

The reason this works is that Firefox is made using XUL, JavaScript and CSS – similar to websites. What you are doing is loading the Firefox XUL environment inside a tab, just as if you were viewing a HTML page on someone’s website.

If you use the Cheevos for Firefox add-on, doing this will award you with a shiny new Cheevo!