Because facebook relies so heavily on javascript, and because we can type javascript into the address bar, that means we can “poke” into the workings of facebook to do things that we wouldn’t normally be able to do. It’s not “hacking” exactly, but it employs the same sort of skills hackers use when looking into applications. The best part is that because it’s all using the same control codes (or “API”) that facebook uses, there’s no way for facebook to find out you’re doing it, so it’s totally safe! (I think…) Besides, we’re not going to be doing anything too dodgy, just a few little tweaks ;)
Facebook Hack: Sending your friends offline
Here’s a funny one; if you’re chatting to a friend, get them to paste the following code into their facebook address bar:

javascript:buddyList.toggleTab();

It’ll make them go offline! Of course it’s not permanent, they can go back online by clicking the icon as normal, or by giving the same command again
Facebook Hack: Change facebook color
Check this out:

Facebook Hack: Change your name (temporarily)
This one’s a very simple hack that you can apply to any website. As you saw in the screenshot above, I’d changed my facebook to display as “Facebook | Leet Hax0r”. You can do this by using the following javascript:

javascript:void(document.title="Facebook | Neo");

Sadly, your friends will only see your actual name, not the new one, but it can make for some amusement in a computer lab class or anywhere where you can show people face to face.

Facebook Hack: Close chat windows
If you’re chatting to a friend and want to close the window, sure you can just click the ‘x’ in the top corner, but isn’t it cooler to do it with javascript? Well no not really, but if you can trick your friend into typing the following code in, you can close the chat window of anyone they’re chatting to:

javascript:chatDisplay.tabs[123132132213].tabXOnClick();

That will close my chat with “123132132213″. You can send your friends that link with your own facebook ID in it, and it’ll close their chat window with you! And if you happen to know that ID:123 is chatting with ID:321, you can send the following to ID:123, and when they paste it in it’ll close their chat with 321!

javascript:chatDisplay.tabs[321].tabXOnClick();

Other Facebook Hacks
The hacks above are the most impressive, but there are a few other little things you can do which are mildly interesting:

Bring up notifications:
javascript:presence.toggleTab('chat_status_control','chat_status_control_tab');

Bring up online friends list:
javascript:buddyList.toggleTab();

Bring up application tab:
javascript:applicationDock.toggleTab();