Guide: Modifying websites and how to say what you really think without sending it.

This is what I wish to see on the Cr-48 tracker.
How can I make this?

I use a firefox extension called Firebug
You can download the newest release here: http://getfirebug.com/releases/firebug/1.7X/

Using this extension is really simple. Just highlight over the selected text and click "Inspect Element".

I have also edited some random person's facebook status to make it more entertaining then something such as: "Shopping, It was fun."

The good part about this add on? Nothing is sent to the person, no one else can see it and a simple refresh of the page will bring everything back to normal.

I'm sure people can think of more mischievous uses for this app.