Now unless you are using IE, you will notice that when you try to click on searchbox and type anything it won't work. The only way to make any input field work is by first right clicking on it and then it will accept input.
The script is basically designed only to work in IE, and it's only working in IE because of bugs only IE has. There's even a snipet of code that tests if you're using IE5 and is supposed to eject an error when you're not, only this isn't even working.
The particular problem you're talking about is caused by (other than only writing for IE5.0) a function that is bound to the mouse events of document that returns false.. blocking all focus() and blur() events. I have now idea why you'd even want that behaviour.