Facebook Chat Tweak

I just wondered if it is possible to change the "new message" sound in a chat window on facebook.

The short answer: Yes it is. Execute the following in your firebug console:

/* 
manually force the chat tab of a certain user to play newMsg sound.
tabs[] 
chatDisplay.tabs[766930143].playSound();
*/

/*
modified playSound method plays any sound you wish
*/
ChatTab.prototype.playSound = function(){
  /* default path: \/sound\/pling.mp3 */
  if(this.chatDisplay.gatedFeatures.sound && chatOptions.getSetting('sound')){
    Sound.play('http://ideadapt.net/Cat Miau.mp3',true);
  }
};

The long answer may follow in some time ...

Also it would be nice to have it packed in a bookmarklet or even a Firefox add-on. Think of a "facebook tweak" add-on that lets you customize the behaviour of various facebook features ...